Method and apparatus for sample analysis

ABSTRACT

Methods and systems for analyzing samples, such as gas samples, are described. One method comprises providing a gas sample, increasing pressure applied to the gas sample to compress the sample to a smaller volume and provide a pneumatically focused gas sample, and analyzing the pneumatically focused gas sample using any of a variety of analytical techniques. Also disclosed are systems for gas analysis, including systems for analysis of pneumatically focused, and thereby concentrated, gas samples and for analysis of particulate matter in gas samples. Analytical systems constructed within personal computer cases also are disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of U.S. patent application Ser. No.09/770,942, filed Jan. 25, 2001, and claims the benefit of U.S.Provisional Patent Application No. 60/177,923, filed Jan. 25, 2000 andU.S. Provisional Patent Application No. 60/448,411, filed Feb. 18, 2003,all of which applications are incorporated herein by reference.

FIELD

The present invention concerns analytical instruments and methods. Moreparticularly, the invention concerns an apparatus for concentration andanalysis of samples, particularly gas samples, and methods formonitoring/analyzing samples using the apparatus.

BACKGROUND

Volatile organic compounds (VOCs) as described by the United StatesEnvironmental Protection Agency (EPA) include components of fuels,solvents, and chemical feedstocks commonly used for internal combustionengine fuel, power and heat generation, cleaning, chemical,pharmaceutical, agricultural, semiconductor and other industries. VOCsare highly regulated in the U.S. and elsewhere in the world because theycontribute to photochemical smog formation. A subset of VOC compoundsincludes those compounds designated by the EPA as toxic chemicals,including those compounds designated as Air Toxics. “Air Toxics” areharmful to breathe. As such they are regulated by the EPA in ambient andindoor air, and by OSHA in the workplace.

Atmospheric VOCs and/or Air Toxics are currently measured under USEPAguidance at regular times and places as part of the PhotochemicalAssessment Monitoring Stations (PAMS). These VOCs may be measuredaccording to EPA Method TO-14A using samples collected in specialcanisters. Another method for measuring Air Toxics or VOCs uses activesampling into sorbent tubes using EPA Method TO-17. In either case thecanisters or sorbent tubes are then transported to a gas chromatographylaboratory for analysis using (for instance) thermal desorption of theadsorbent cartridges, or flushing or pumping from the canisters. This isfollowed by cryogenic or some other type of cooling. Detailedinstructions on these procedures are freely available from the USEPA,which publishes the TO-xx methods. Gas chromatography methods for airanalysis are recently summarized in an extensive review article writtenby Detlev Helmig, entitled “Air Analysis by Gas Chromatography,” Journalof Chromatography A, 843:129-146 (1999).

Harmful or toxic chemicals based upon organic chemicals typically have acarbon skeleton and usually are derived from petroleum. The simplestmembers of this wide range of compounds are hydrocarbons (HC's),compounds containing only the elements carbon and hydrogen. Hydrocarbonsconsist of alkanes (all single bonds), alkenes (at least onecarbon/carbon double bond), alkynes (at least one carbon/carbon triplebond), and aromatics, which contain conjugated carbon/carbon doublebonds, and are derivatives of benzene, C₆H₆. These bondingfunctionalities may exist in combination with one another, making anindividual hydrocarbon belong to more than one class. There is no strictupper limit to the molecular weight, molecular size, or carbon number ofsuch compounds. As the carbon number increases, the compounds havedecreasing vapor pressure and, if present in the atmosphere at all, areincreasingly present in suspended particulate matter rather than asgases. Table I provides exemplary members of each HC family.

TABLE I Examples of Hydrocarbons Classified as VOCs Alkanes AlkenesAlkynes Aromatics 1. Methane 1. Ethene 1. Ethyne 1. Benzene (C6H6) (CH4)(C2H4) (C2H2) 2. Ethane 2. Propene 2. Propyne 2. Methylbenzene (C2H6)(C3H6) (C3H4) (C7H8), i.e., toluene 3. Propane 3. Butene 3. Butyne 3.Ethylbenzene (C3H8) (C4H8), (C4H6), (C8H10) which which exists in existsin isometric isomeric forms forms 4. Butane 4. Butadiene 4.Dimethylbenzene (C4H10), (C4H6) (C8H10), i.e., which xylene, whichexists in exists in isomeric isomeric forms forms 5. Naphthalene (C10H8)

Other VOC compounds include carbon, hydrogen, and at least one otherelement, especially including (but not limited to) the elements oxygen,sulfur, nitrogen, phosphorus, and the halogens, such as fluorine,chlorine, bromine and iodine. Such compounds are used in the chemical,electronics, agricultural, and many other industries as solvents,pesticides, drugs, and so forth. Compounds containing the elements C, H,and O are sometimes called oxygenated volatile organic compounds, OVOCs.Table II provides a few exemplary members of this extended VOC family.

TABLE II Examples of VOCs other than Pure Hydrocarbons Oxygen-containing OVOCs Sulfur-Containing Halogen-Containing 1. Aldehydes 1.Sulfides 1. Chlorocarbons (e.g., CHCL3, CH2C12, CH3C1, CH3CC13, C2C14 2.Ketones 2. Sulfates 2. Halons (e.g., CH3Br, CH3I) 3. Acids 3. Mercaptans3. Chlorofluorocarbons (e.g., CC12F2, CC1F3, CC14, CF4) 4. Ethers 4.Thiols 5. Alcohols

A partial listing of chemical compounds found in the atmosphere isChemical Compounds in the Atmosphere, (1978) Academic Press, T. E.Graedel. This book lists many hundreds of such compounds known when itwas published more than 20 years ago.

A major source of atmospheric hydrocarbons is automobile gasoline, whichtypically contains hydrocarbons having carbon numbers greater than 3.Methane, natural gas, is widespread and relatively constant in theatmosphere at concentrations of about 1.8 ppm by volume. Natural gas isabout 95% methane and 5% ethane. Propane makes up the bulk of liquefiedpetroleum gas (LPG). Gasoline and diesel fuel and their resultingcombustion byproducts together contain more than 200 individualhydrocarbons. See Fraser et al., “Air Quality Model Data Evaluation forOrganics. 4. C2-C36 Non-aromatic Hydrocarbons,” Environ. Sci. Technol.,31:2356-2367 (1997). Since these compounds, along with oxides ofnitrogen also produced in combustion, react chemically in the atmosphereto produce smog, there is worldwide interest in controlling theiratmospheric emission, and in measuring their individual (speciated)concentrations.

Air Toxics are compounds directly harmful to human health, and the EPAhas many regulations dealing with their emission and atmosphericconcentration. Efficient measuring of ambient concentrations is highlyimportant. All ambient gaseous compounds also appear in human breathsince they are inhaled. In addition, metabolic processes add additionalvolatile compounds to exhaled breath, such as ethanol, acetone,isoprene, pentane and others. Study of metabolic processes ofrespiratory organisms and diagnosis of disease would benefit greatlyfrom automated VOC analysis in exhaled air. Chromatographic analysis ofanesthesia environments such as hospitals has been reviewed by A Uyanikin Journal of Chromatography B 693 (1997) 1-9. From this review it isclear that a sensitive, inexpensive, compact gas chromatograph would bea useful tool for operating rooms and associated environments.

Sick Building Syndrome involves poorly characterized human diseases andailments associated with outgassing of toxic materials in the indoorenvironment. Sources of such toxic materials can include carpets,drapes, particle board, etc. Harmful fungi and bacteria which can thrivein moist or poorly ventilated environments often emit characteristic VOCor OVOC compounds (e.g. heptanol) which, although they may not be toxicthemselves, can serve as indicators of the presence and abundance ofsuch harmful organisms.

Chemical synthesis or process streams, clean rooms and other industrialareas require automated, sensitive gas analysis procedures which may beroutinely implemented for reasonable costs. Other areas which wouldbenefit from highly sensitive analytical air analysis methods would bethose areas dealing with naturally occurring and artificially appliedpheromones for insect attraction and/or control.

In sampling trace level VOCs, air toxics, metabolites or other analytessuch as particulates in the atmosphere, in breath, or other gaseousenvironments, the concentration of target analytes often is below thedetection limit of a particular analytical technique. Such analysis isoften termed trace gas analysis. A wide range of concentrations may bepresent, for instance from 1 ppmV (1 part per million by volume) down to1 pptV—a range of one million. For instance, in gas chromatography, aflame ionization detector cannot detect many VOCs of ambient atmospheresor in breath samples unless they are concentrated. Two concentrationmethods are commonly employed: (a) cryogenic focusing/concentration and(b) adsorbent focusing/concentration. In each method an air sample ofthe desired volume is passed through an accumulation chamber, whichconsists of:

-   -   (a) a ‘U-tube’ immersed in a cryogenic liquid, such as liquid        oxygen or air, or which is otherwise cooled sufficiently that        some or all of the target analytes condense to liquids or solids        within the U-tube trap, also referred to herein as a cryotrap.        Most of the air sample does not condense and therefore passes        through the trap; or    -   (b) a sorbent-filled trap, which absorbs or adsorbs some or all        of the target analytes, allowing most of the sample to pass        through. Such traps can operate at ambient temperature or below.

Either procedure concentrates the desired analytes to a concentrationmuch higher than their original concentration in the air sample. Afterthe desired air volume has passed through the trap, yielding sufficientanalyte, the trap is heated to transfer the concentrated analytes into achromatographic column or other analytical device.

Both of these procedures are commonly used in the field of atmosphericanalysis, air pollution, etc. However, each has drawbacks, which makesthem less amenable to automating an air-monitoring instrument,especially for field use. In the case of cryogenic focusing, thecryogenic liquid must be stored on site and pumped as needed forcryogenic focusing. Although electrically cooled devices are available,such devices typically cannot obtain sufficiently low temperatures tocollect all of the VOCs that can be condensed by cryogenic focusing.Another problem with cryofocusing is the large amount of atmosphericmaterials, particularly water and carbon dioxide, which are trappedalong with desired analytes, unless separately removed before thecryotrap. Yet another problem with cryofocusing is that such instrumentstypically reside in laboratories to which samples must be transported inspecial containers. Although such transport has been extensivelystudied, there remains the possibility of sample modification so thatspurious compounds may either be added to or subtracted from transportedand/or stored samples. For sorbent-filled traps, the sorbent materialmust adsorb and desorb a wide range of potential analytes because thetarget analyte volatilities vary greatly. A strongly absorbent materialmay collect all analytes, but temperatures high enough to causedesorption of the least volatile analytes may cause decomposition ofanalytes or the absorbent collecting material itself. A less absorbentmaterial may sorb and desorb the heavier analytes, but not collect themore volatile analytes, which therefore are not completely collected.Another problem with sorption is the tendency for the material to desorbover a period of time when heated. This can require refocusing withcryogens or other methods during analysis. Sorbent and cryofocusing canbe used in combination. A final problem with adsorbents is possiblechemical reaction or decomposition of the target analytes duringcollection, transport or storage of the adsorbent cartridges, or thepresence of artifacts acquired on the adsorbents before or aftersampling. Such artifacts are not uncommon in atmospheric sampling andoften lead to spurious conclusions about atmospheric trace-gascomposition. Ambient air sampling and breath analysis would benefitgreatly from in-situ, continuous, real time analytical instrumentation.Such instrumentation is not widely available nor currently practical.

Gas chromatography methods for air analysis are recently summarized inan extensive review article written by Detlev Helmig, entitled “AirAnalysis by Gas Chromatography,” Journal of Chromatography A,843:129-146 (1999), which is incorporated herein by reference. Helmig'sreview substantiates the conclusion that only two primary methods areknown for concentrating analytes in an ambient air sample, cryofocusingand absorbent traps. These methods are poorly amenable to developingremotely operated, continuous sampling methods for ambient air althoughsuch methods have been reported. For instance J P Greenberg, B Lee, DHelmig and P R Zimmerman have described a “Fully automated gaschromatograph-flame ionization detector system for the in situdetermination of atmospheric non-methane hydrocarbons at low parts pertrillion concentration” in Journal of Chromatography A 676 (1994) pp.389-98. This system was designed to (1) rapidly trap air samples of upto 4 liters volume to allow for sub-parts per trillion detection limits,(2) eliminate interferences from ambient ozone, water vapor and carbondioxide, and (3) reduce to negligible levels any contamination in theanalytical systems, and (4) allow for continuous unattended operation.This instrument used cryogenic sample freeze-out and was successfullyemployed for measurements in the state of Hawaii. However, it apparentlyhas seen limited additional use since that time, probably because of itscost, complexity and use of cryogenic fluids.

Other pertinent areas include breath analysis. For instance, U.S. Pat.No. 5,293,875, “In-vivo Measurement of End-tidal Carbon Mono xideConcentration Apparatus and Methods” describes a noninvasive device andmethods for measuring the end-tidal carbon monoxide concentration in apatient's breath, particularly newborn and premature infants. Thepatient's breath is monitored. An average carbon monoxide concentrationis determined based on an average of discrete samples in a given timeperiod. An easy to use microcontroller-based device containing a carbondioxide detector, a carbon monoxide detector and a pump for use in ahospital, home, physician's office or clinic by persons not requiringhigh skill and training is described.

K D Oliver and 7 co-authors of Mantech Environmental, the USEPA, XonTechand Varian Chromatographic Systems have described a “Technique forMonitoring Toxic VOCs in Air: Sorbent Preconcentration, Closed-CycleCooler Cryofocusing and GC/MS analysis” in Environmental Science andTechnology 30 (1996) 1939-1945. This powerful but very complex,automated system usually is attended by various operators and has seenonly intermittent field use, perhaps due to operational expense andcomplexity.

Air pollution is increasingly regulated throughout the world. Knowingthe source of pollution emissions is essential to this regulatoryprocess so that regulation can be efficient and cost effective. Onemethod for determining air pollution sources is source characterization.That is, individual sources are surveyed either by direct measurementsof emissions or by apportionation by generic emission factors. Usuallylocal, regional, or national pollution control agencies maintainemission inventories and issue emission permits. Such emissioninventories are widely viewed as unreliable. Once emission factors for avariety of pollutant species, including VOCs, are available, individualmeasurements of atmospheric VOCs at any site can be assignedquantitatively to the major sources by mathematical processes referredas Source Apportionment or Chemical Element Balances. Efficient,cost-effective measurements of ambient VOCs, Air Toxics, and otherpollutant concentrations will allow this source apportionment procedureto be carried out more efficiently. Beyond source apportionment,recently developed computer programs (program UNMIX developed by Dr.Ronald Henry of the University of Southern California) now allow sourcesto be determined from ambient VOC measurements without any direct sourceinformation. (See ScienceNewsOnline Jun. 28, 1997 and the USC ChronicleSep. 1, 1997, included herein) As Dr. Henry describes it, these programsallow the ambient air data to analyze itself. This extremely powerfulnew mathematical technique would benefit greatly from lowcost, andtherefore frequent measurements of VOCs and other such compounds inpolluted air.

In addition to the organic compounds discussed above, there is a needfor the determination of various inorganic atmospheric constituents. Afew examples are NO, NO₂, SO₂, H₂S, O₃, CO, etc. Many of these havespecific instrumental methods and measurement devices devotedspecifically to their determination, for instance in automobile testingas well as in ambient air. A more general method involves measurement ofone or more of such species (including VOC and OVOC compounds discussedabove) by light absorption. This may occur typically in the ultraviolet,visible, or infrared. When species are present at very lowconcentrations, often long path lengths are used. This may involvemeters or kilometers through the open atmosphere, or reflected paths ina localized instrument. Examples of such techniques are differentialoptical absorption spectroscopy (DOAS) and Fourier transform infraredspectroscopy (FTIR). Such instruments may determine one or manyatmospheric components simultaneously using light at various suitablewavelengths.

Despite these previously developed techniques and inventions, therestill is a need for an apparatus and method for continuous, and remoteif desired, concentration and analysis of gaseous samples. Such a methodand apparatus, if available, would allow automation of methods foranalyzing analytes in a gaseous sample, such as air-pollution analysis,clinical breath analysis, metabolic studies, process streams, cleanrooms, etc.

SUMMARY

The disclosed embodiments address the problems and shortcomingsassociated with the prior methods and apparatuses described in theBackground section, and provide many advantages relative to priormethods and apparatuses directed to potentially continuous spectrometricor GC analysis of gaseous samples. For example, Pneumatic Focusing asdescribed herein operates very rapidly as pressurization and transit ofthe sample through a chromatographic column are inherently very fast dueto the high pressure driving the analysis. The speed of the analysis canbe adjusted by adjusting a Pneumatic Focusing valve, which controls thecolumn flow rate. All features can be controlled by a computer tooptimize the most important parameters. Hence, the present technologyallows for the development of portable, compact, fast, multi-detector,multi-column instruments that can be used, if desired, for continuouslyobtaining and analyzing a pneumatically focused gas sample.

The method does not require cryofocusing, or sorbent-trap focusing, aswith prior methods, although it should be appreciated that the presentmethod can be practiced in combination with cryofocusing and/orsorbent-trap focusing of analytes in laboratory or field use. Forexample, cryofocusing a sample after it has been pneumatically focusedmight provide better resolution than is achieved by practicing eithermethod separately, particularly for the more volatile analytes beinganalyzed. In a chromatographic system, a sample is separated intocomponents which then must be delivered to a suitable analytical device(such as a FID, an ECD, etc) for detection and quantification. PneumaticFocusing is advantageous for concentrating such samples before injectioninto the chromatographic column. Pneumatic Focusing is equallyapplicable for direct introduction of a sample into an analyticaldevice, such as a UV-VIS or IR absorption cell, in which case achromatographic column need not be employed. One chief advantage andapplication of Pneumatic Focusing is it's applicability to trace gasmeasurements. Atmospheric trace gases range in concentration frommethane (1.8 ppm in the global troposphere) down in concentration to ahost of species at the ppt (0.000001 ppm) level in clean air. A similarconcentration range is undoubtedly present in exhaled breath. Many suchbreath components are present in inhaled air, but a variety of exhaledmetabolites are of real interest because of diagnostic information theycould provide. Important metabolites and disease markers may be presentat very low concentrations and may be difficult to distinguish fromcompounds already present in inhaled air.

Pneumatically focused chromatography represents a superior approach toprior measurements, such as those described above concerning EPAmeasurements. This is because Pneumatic Focusing is more easilyautomated for laboratory analysis of such VOCs or Air Toxics fromcanisters or sorbent tubes, or most especially, to real-time,continuous, in-the-field sampling of these gases wherein the problemsand artifacts associated with sample collection, transport and storageare mitigated or eliminated altogether. The advantage of PneumaticFocusing is that it is simpler, more easily automated, less prone toartifacts, more easily calibrated and can provide more extensivemeasurements of atmospheric VOCs, Air Toxics, breath components, etc. atless cost than with present methods.

A method for analyzing a gas sample comprises providing a gas sample,increasing pressure applied to the gas sample to compress the sample toa smaller volume and provide a pneumatically focused gas sample, andthereafter analyzing the pneumatically focused gas sample, such as byusing a gas chromatograph or spectrometric cell. Typically, the gassample is pneumatically focused prior to or concurrently with reaching aseparatory column or spectrometric cell. The method is well suited foranalyzing ambient air samples, both continuously, and can be, but doesnot necessarily have to be, run remotely using computer control andtelemetric data transfer. Continuously sampling ambient air provides amethod for real-time monitoring of indoor or outdoor air quality or forin-situ clinical analysis of breath samples from subjects or patients.

As used herein, Pneumatic Focusing generally means increasing thepressure of a gaseous sample from a starting pressure (e.g. atmosphericpressure) to a pressure of from about 100 psi to about 15,000 psi, moretypically from about 200 psi to about 2,000 psi, with workingembodiments having been practiced primarily at Pneumatic Focusingpressures of from about 250 psi to about 500 psi in the case of gaschromatography and from 150 psi to 2,000 psi in the case of absorptionspectroscopy. Pneumatic Focusing can be carried out with a sampleoriginating as a gas, in which case the sample may be focused(pressurized) in a sample cell or concurrently as it is introduced to achromatographic column or spectrometric cell. Pneumatic Focusing mayalso be carried out with a liquid sample vaporized at an effectivevaporization temperature upon introduction into a gas chromatograph orheated spectrometric cell. In either case high pressure in the samplingor analytical environment will serve to focus (concentrate) the samplefor better detectability of the target analytes. One goal of PneumaticFocusing is to allow introduction of large quantities of analytes intoanalytical devices. Another goal is the removal of undesired condensablevapors, such as water vapor. When used with gas chromatography we callthis procedure Pneumatic Focusing Gas Chromatography (PFGC). The methodalso can comprise reducing the pressure of the carrier gas, such as topressures below about 100 psi, simultaneously with or subsequent to thepneumatically focused sample being injected onto a separatory column sothat the chromatography occurs at more normally employed pressures. Inthe case of spectroscopy, Pneumatic Focusing can mean continuously ordiscretely increasing the pressure of a gaseous sample either in, orbefore entrance into, a spectrometric cell so that absorbances areadjusted to an optimum level for enhanced signal-to-noise ratio andimproved sensitivity. Pneumatic Focusing also can comprise suddenlyincreasing or decreasing the pressure between a higher and a lowerpressure for observation of transient absorptions that are notobservable at constant high or low pressure. In one working embodimentin a uv/visible light absorption cell, pressure was abruptly increasedfrom ambient (˜15 psi) to pressures ranging from 150 to 2000 psi.Pressure was also abruptly dropped within the same range of pressures.Transient absorbances occurring during these pressure transients can beuseful in measuring concentrations of trace absorbers or in studyingnucleation processes or in measuring concentrations of nucleatingaerosols, such as biological aerosols, including spores. The apparatuswhere Pneumatic Focusing (or defocusing) is carried out can be eitherheated or cooled from ambient temperatures to prevent or enhance suchaerosol nucleation, or to enhance or retard adsorption or absorption tothe surfaces of the apparatus. The region of a device in which PneumaticFocusing is carried out may include but is not limited tochromatographic columns, sample loops for chromatographic columns,spectrometric light absorption or scattering cells, electromagneticwaveguides, such as optical or infrared waveguides, etc.

Condensable vapors (such as water vapor which may interfere with ananalysis) may be removed in a prefocusing prechamber if desired beforethe sample is introduced to the light absorption chamber orchromatographic column. Such vapors may be either discarded or analyzedseparately by automated transfer to additional analytical devices.

Spectrometric measurements are normally interpreted in terms of theBeer-Lambert Law I=I_(o)e−^(ac1) or alternately I=I_(o)10−^(a′c1) wherea is the absorption coefficient, c is the absorber's concentration and 1is the path length. Using this law, previously measured and recordedabsorption coefficients, a measured path length, and an experimentallymeasured absorbance Io/I, it is common practice to determine theconcentration c of an analyte. Thus absorption responds to the productof concentration and path length.

In carrying out Spectrometric Pneumatic Focusing (SPF) it is possible tocontrol with a combination of temperature and pressure the dispositionof various condensable or adsorbable vapors in a confined sample or in acontinuous sample stream. When pressure of a gaseous mixture isincreased, as in Pneumatic Focusing, the absorptivity of target analytesmay change in ways not obvious from a consideration of Beers Law. Forinstance, in preliminary investigations of Pneumatic FocusingSpectroscopy all of the following have been observed when pressure wasgradually increased or decreased:

-   -   1. The absorbance increases linearly with pressure due to        increasing concentration as expected from Beer's Law.    -   2. The absorbance increases proportional to the square root of        the pressure ratio due to dimerization of the target analyte to        produce a nonabsorbing dimer.    -   3. The absorbance increases proportional to the square of the        pressure ratio due to absorption of dimers or collision        complexes.    -   4. The absorbance increases and remains constant due to        condensation of the target analyte to a liquid which is removed        from the view of the absorbed light beam.    -   5. The absorbance may increase, decrease, or otherwise behave        erratically due to phenomena not currently understood.    -   6. Continuous oscillations in cell transmission which were        wavelength dependent.

When the Pneumatic Focusing pressure was increased or decreased suddenlyadditional phenomena have been observed, some of which may be due tonucleation and/or growth of light scattering aerosols.

Heating and/or cooling a separatory column subsequent to injecting thepneumatically focused sample also could be advantageous. For example,the method may involve cooling a head portion of the column prior toinjecting the pneumatically focused sample onto the column and heatingthe column subsequent to injecting the pneumatically focused sample ontothe column.

In chromatography plural eluting gasses can be used to elute thepneumatically focused sample. For example, the method may involveeluting a pneumatically focused sample with a first carrier gas, andthen eluting the column with a second carrier gas. And, either the firstor second gas (usually the second) may be a supercritical fluid. See SPentoney et al., “Combined Gas and Supercritical Fluid Chromatographyfor the High Resolution Separation of Volatile and NonvolatileCompounds,” Journal of Chromatographic Science, 5:93-98 (1987). It couldalso be advantageous after Pneumatic Focusing to drop the columnpressure to lower values and then gradually increase it again, graduallyswitching from a non-supercritical to a supercritical fluid for betterelution of analytes through the column. Such approach could in someinstances obviate the need for temperature programming of the columnwith resultant reduction in power requirements to facilitate portabilityand field operation.

The method can involve continuous sampling. This embodiment provides aconsiderable amount of data. This collection of data allows individualchromatograms, collected over time, to be averaged. This can, forexample, provide a well-defined, stable baseline so that analyte peaksare easier to discern, identify and quantify, thereby increasingsensitivity. Once peak locations are established on a low-noise,averaged chromatogram, these peak locations may be used to unambiguouslyidentify the position of individual low-intensity peaks on theindividual chromatograms which formed the average. This can improve thesensitivity and lower the limit of detection.

The method can be practiced with various detectors. A working embodimentused a flame ionization detector. However, most commercially availabledetectors can be used in combination with a system for pneumaticallyfocusing a gas sample as described herein. Additionally, the method canbe practiced using plural separatory columns connected in series, or inparallel. The method can be used in combination with other techniquescurrently known or hereafter developed for focusing analytes in a gassample. For example, Pneumatic Focusing can be done in combination withcryofocusing, absorbent focusing, or both. Pneumatic Focusing can alsobe carried out in a suitably designed spectrometric cell which alsoserves as the sample loop (injection volume) for a chromatographic orother system so that spectroscopic properties of the sample may bedetermined prior to separation and analysis chromatographically or byother means. Such approach would be beneficial, for instance, indetermining the total hydrocarbon content of a VOC sample by application(without limitation) of nondispersive infrared analysis to the CH bondregion of the spectrum. Gasses may be passed at high pressure through aspectrometric cell after separation and elution from a separatory columnas well.

A gas chromatograph and gaseous sample analysis system also isdisclosed. One embodiment of the system comprised: a sample loop forreceiving a first volume of a gaseous sample; a separatory columnfluidly connected to and downstream of the sample loop; an inlinepressure-increasing valve downstream of the separatory column, whichincreases system pressure to pneumatically focus the gaseous sample andadjust flow rate through the system. Flow rate can be adjusted asdesired to be substantially about the same linear flow rate through thesystem as prior to increasing the pressure with the inline valve, lessthan the linear flow rate through the system prior to increasing thepressure with the inline valve, or greater than the linear flow ratethrough the system prior to increasing the pressure with the inlinevalve; and a detector downstream of the pressure increasing valve fordetecting analytes. The system can further comprise plural samplecollection coils, and plural separatory columns, connected either inparallel or in series with appropriate switching, heart-cutting,2-dimensional chromatographing or other manipulation of the analytesduring separation and analysis. In one working embodiment, a single airsample distributed into two separate sample loops was simultaneouslyinjected into two different separatory columns, one more suitable forVOC compounds and the other for OVOC compounds. In this way a broaderrange of compounds in polluted air or in human breath could be analyzed.For continuous monitoring of ambient air, the system typically includesa sample collection pump for continuously drawing the gaseous sampleinto the gas sample collection coil. The system has been automated byplacing its operation under computer control. Moreover, the technique ofpneumatically focusing can be used in combination with gaschromatographs located on microchips, which GCs should be modified toaccept higher gas pressures.

For analysis of human breath, one working embodiment used a speciallydesigned breath-sampling device. A 100 cc-glass syringe was fluidlyconnected to the previous dual column gas chromatograph. The lastportion of a human breath was collected into the syringe by the subjectbreathing through a Teflon tube through a 4-way valve to inflate thesyringe. This syringe exerts much less back pressure than the sampleloop itself and is easier for a subject to breathe into. After thesyringe was filled with breath, the 4-way valve was switched and thesample pump then drew the breath sample into the sample loops over aperiod of 20-40 seconds. Once the sample had passed from the samplingsyringe into the sample loops it was pneumatically focused into thechromatograph for analysis of the VOCs and OVOCs and other compounds inthe human breath. Such instrumentation will be useful in diseasediagnosis or in analysis of metabolic processes in humans or otherrespiratory organisms. One advantage of this syringe sampler is minimalexposure of the syringe walls to the breath sample as the syringeremains ‘closed’ at all times except for the approximately 1 minuteinvolved in sampling. Thus, current analytes or leftover analytes fromprevious samples have a minimum amount of time to exchange with thewalls and be either removed from or added to a breath sample. Anadditional advantage is that the breath sample provider (such as amedical patient or subject) obtains visual feedback on the course ofsample delivery and transfer to the chromatographic or other analysisdevice.

Also disclosed are Methods and systems for measuring the concentrationof particulates, such as spores, in a gas sample are described. Thedisclosed methods constitute simple, inexpensive approaches that may beeconomically implemented on a widespread basis to provide early warningof the presence of potentially infectious spores. Such spores may benaturally present in some environments, such as mold-infected buildingsor other environments, or could be deliberately introduced by terroristsor other criminals.

Also disclosed are methods of selectively condensing water vapor onbiological aerosols present in indoor or outdoor air. In one embodiment,the condensation process is used to grow the size of such aerosols sothat they can be individually visualized in a light beam and viewed withan inexpensive computer-based camera, commonly called a webcam.

In another aspect, instrumentation constructed within a personalcomputer case is provided. Such instrumentation includes pneumaticfocusing systems (for chromatography and spectroscopy) and particledetection systems, as well as gas chromatography/mass spectrometrysystems, and other spectrophotometers, such as infrared and fluorescencespectrophotometers. Examples of personal computer cases that may be usedto construct the instrumentation include full towers, mid-towers, anddesktop cases. Further examples of suitable personal computer casesinclude AT, BATX, ATX, MATX, LPX and microATX compatible cases. In aworking embodiment, a pneumatic focusing gas chromatograph isconstructed in an ATX compatible tower case.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a system for pneumatically focusing andanalyzing a gaseous sample.

FIG. 2 is a schematic diagram of a one embodiment of a high pressurespectral analysis system.

FIG. 3 is a schematic diagram of a working embodiment of a device forcontinuously providing sample to a focusing system.

FIG. 4 is a cross sectional view of the system illustrated in FIG. 3.

FIG. 5 is a schematic diagram of a working embodiment of a check valve.

FIG. 6 is a schematic diagram of a continuous Pneumatic Focusing system.

FIG. 7 is a schematic of a chromatograph useful for making and using adisclosed embodiment of a chromatograph for pneumatically focusingsamples.

FIG. 8 is a schematic drawing of an apparatus useful for injection ofliquid samples for Pneumatic Focusing.

FIG. 9 is a schematic drawing of a pressure increasing/linear flowreducing valve.

FIG. 10 is a schematic drawing of a pressure increasing/linear flowreducing valve.

FIG. 11 is a schematic drawing of a needle valve for pressure/flowfeedback.

FIG. 12 is a control circuit for an A/D board.

FIG. 13 is an amplifier circuit used to increase voltage of signals froman A/D board.

FIG. 14 is a schematic drawing of system for controlling valves.

FIG. 15 is a chromatogram illustrating a method for determining a truebase line for chromatograms produced by a disclosed apparatus andmethod.

FIG. 16 is a graph of analog offset to an A/D board.

FIG. 17 is a graph of interpolation between digital readings on an A/Dboard.

FIG. 18 is an enlargement of the digital data from FIG. 17.

FIG. 19 is a block diagram of a program to integrate chromatographicpeaks.

FIG. 20 shows output from the program integpro.bas.

FIG. 21 is a chromatogram illustrating using methane as an internalstandard.

FIG. 22 is an apparatus to determine a true chromatographic baseline.

FIG. 23 is a schematic drawing of a pneumatic piston.

FIG. 24 is a graph illustrating the continuous, real-time collection ofatmospheric data using a disclosed apparatus with the methane peak beingattenuated by a factor of 100.

FIG. 25 is an averaged chromatogram as prepared for the 40 pluralchromatograms of FIG. 24.

FIG. 26 is one chromatogram of the plural chromatograms provided by FIG.24 with the methane peak being attenuated by a factor of 100.

FIG. 27 is a chromatogram produced using a dual column and an embodimentof a disclosed apparatus.

FIG. 28 is a chromatogram of a gasoline sample (0.000001 liters liquidgasoline in 847 liters of air with about 3 ppm methane) made at 200 psiusing a disclosed apparatus and method.

FIG. 29 is a chromatogram of a gasoline sample (0.000001 liters liquidgasoline in 847 liters of air with about 3 ppm methane) made at 250 psiusing a disclosed apparatus and method with the methane peak beingattenuated by a factor of 10.

FIG. 30 is a chromatogram of a gasoline sample (0.000001 liters liquidgasoline in 847 liters of air with about 3 ppm methane) made at 350 psiusing a disclosed apparatus and method with the methane peak beingattenuated by a factor of 100.

FIG. 31 chromatogram of a gasoline sample (0.000001 liters liquidgasoline in 847 liters of air with about 3 ppm methane) made at 400 psiusing a disclosed apparatus and method with the methane peak beingattenuated by a factor of 100.

FIG. 32 chromatogram of a gasoline sample (0.000001 liters liquidgasoline in 847 liters of air with about 3 ppm methane) made at 500 psiusing a disclosed apparatus and method.

FIG. 33 is a chromatogram of a gasoline sample (0.000001 liters liquidgasoline in 847 liters of air with about 3 ppm methane) made at 900 psiand 30 standard cubic centimeters/minute flow rate using a disclosedapparatus and method.

FIG. 34 is a chromatogram of a gasoline sample (0.000001 liters liquidgasoline in 847 liters of air with about 3 ppm methane) made at 900 psiand 40 standard cubic centimeters/minute flow rate using a disclosedapparatus and method.

FIG. 35 is a chromatogram of a gasoline sample (0.000001 liters liquidgasoline in 847 liters of air with about 3 ppm methane) made at 900 psiand 60 standard cubic centimeters/minute flow rate using a disclosedapparatus and method.

FIG. 36 is a chromatogram of ambient air in Portland, Oreg., during aperiod when wind speeds varied from about 30 miles per hour to about 80miles per hour with the methane peak being attenuated by a factor of100.

FIG. 37 is an average of 10 chromatograms taken during the wind stormbefore and after the chromatogram of FIG. 36 with the methane peak beingattenuated by a factor of 100.

FIG. 38 is an average of 37 chromatograms of ambient air in Portland,Oreg., for polluted air as a reference to FIGS. 36 and 37 with themethane peak being attenuated by a factor of 100.

FIG. 39 is a circuit diagram for a disclosed system for sampling breathusing a syringe.

FIG. 40 is a chromatogram of breath exhalations illustrating thereproducibility of the chromatograms.

FIG. 41 is a chromatogram of breath exhalations from another person.

FIG. 42 is a chromatogram of breath exhalation from a person indicatingmetabolic effects.

FIG. 43 is a chromatogram of breath exhalations illustrating thedetection of alcohol following consumption.

FIG. 44 is a chromatogram of breath exhalations from two heavy smokers.

FIG. 45 is a calibration curve.

FIG. 46 is a chromatogram of acetone focused to 1,000 psi.

FIG. 47 is chromatogram of benzene focused to 1,500 psi.

FIG. 48 is a chromatogram illustrating determination of a sample andaccounting for wind direction.

FIG. 49 illustrates pneumatic focusing of acetone at pressures of 15 to600 psi.

FIG. 50 shows variations in light transmission with wavelength.

FIG. 51 is a diagram showing a rear view of a personal computer casemodified with a particular layout of inlet ports for sampling and gaslines

FIG. 52 is a diagram showing a side cutaway view of a modified personalcomputer case housing components of both a personal computer and apneumatic focusing gas chromatograph.

FIG. 53 is diagram showing a rear view of a personal computer casemodified with another particular layout of inlet ports for sampling andgas lines, and flow control valves, for including a pneumatic focusinggas chromatograph in the case.

FIG. 54 is a diagram showing a side view of a pneumatic focusing gaschromatograph including a piston inlet that is constructed within amodified personal computer case.

FIG. 55 is diagram showing a side view of an embodiment of a pistoninlet assembly.

FIG. 54 is a diagram showing a side view of another embodiment of apiston inlet.

FIG. 57 is a diagram showing an a check valve and crimp flow regulator.

FIG. 58 is diagram showing a side view of an embodiment of a checkvalve.

FIG. 59 is a diagram showing an embodiment of a crimped flow controlfitting.

FIG. 60 is a diagram showing connections and circuitry of a system forvisualizing, identifying and counting spores in a gas sample.

FIG. 61 is a cross-section of the end of a compression cylinder.

FIG. 62 is a detailed magnification of a fitting used to secure a webcamera to the compression cylinder of FIG. 62.

FIG. 63 is a graph showing particle counts obtained in three separateexperiments using ordinary room air as a sample, and two samples whereroom air was passed through a small jar containing spores formed by moldgrowing on a carbohydrate medium. Also shown are the web camera imagesof the aerosol particles produced by compression/condensation of the airsamples in the apparatus illustrated in FIGS. 60-62.

FIG. 64 is a set of web camera digital images of hydrated spores taken{fraction (1/30)} second apart.

FIG. 65 is a set of web camera digital images of hydrated spores taken ⅓second apart. These images were made by selecting every 10^(th) imagefrom web camera images taken as in FIG. 64.

DETAILED DESCRIPTION

The present invention was developed to provide analyticalinstrumentation and methods for analysis of samples, particularly gassamples. For example, systems for measuring gaseous and particulatecomponents of a gas sample, such as an air sample are disclosed. Methodsand systems for concentrating samples for analysis also are disclosed.The disclosed analytical instrumentation also includes a variety ofanalytical systems constructed within personal computer cases.

In some embodiments, the disclosed systems and methods overcome thelimitations of prior trace gas-measurement technologies and providemoderately priced, sensitive, automated trace-gas measurement devicescapable of both batch and continuous operation. One feature of suchdevices is referred to herein as Pneumatic Focusing. Pneumatic Focusingrefers generally to providing a gas sample at a first volume andpressure and compressing the sample to a second smaller volume andhigher pressure. Goals of such compression may include withoutlimitation.

-   -   1. Providing higher sensitivity for sample determination due to        increased concentration.    -   2. Removal of undesired or interfering components of the sample        due to condensation or adsorption (e.g. water removal)    -   3. Delivery of such condensables to additional analytical        instruments for separate chemical analysis.    -   4. Initiating the nucleation and/or growth of aerosols whose        spectroscopic properties of absorption and scattering of various        wavelengths of light will yield additional information about the        sample's physical and chemical composition.    -   5. Providing better resolution by confining the sample to a        smaller volume which may be more effectively separated on a        chromatographic column.

In addition to the previous Pneumatic Focusing goals, temperature may bemanipulated in a pneumatically focused gas sample (without limitation)for any of several reasons, including.

-   -   1. Heating the sample focusing cell, chromatographic column or        spectrometric cell to prevent condensation of selected vapors.    -   2. Cooling same or portions of same to enhance condensation of        selected vapors.

Compressing a gaseous sample, such as an air sample, from a firstpressure to a second higher pressure refers to first pressuresconventionally used in gas chromatography, such as less than 100 psi,and typically less than about 60 psi. The first pressure may be, forexample, atmospheric pressure ˜15 psi (or less at elevation) as is oftenused in spectrometric analysis of air or breath and the second pressuremay range from 150 to 15,000 psi. A sample containing an analyte at afirst concentration is compressed sufficiently so that the analytes,which are to be detected in the sample, reach a second, higherconcentration, which is more easily measured by a detector. Finalpressures will vary depending upon the particular application and uponthe chromatographic or spectrometric properties of the target analytes.For instance, mathematical analysis of the absorption process accordingto Beer's Law indicates that a particular absorbance level provides thebest sensitivity and highest signal to noise ratio in absorptionspectrometry. Pneumatic Focusing may adjust the absorptivity of asample, successively and continuously, to maximize the sensitivity toone or several individual component analytes.

I. Analytical Chemistry Terms Defined

The field of analytical chemistry concerns itself with measurement ofthe concentrations of various substances. This can include eitherroutine measurements using established techniques or the development ofnew or innovative techniques. In some cases these substances are presentat very low concentrations. Such analysis then might be termed ‘traceanalysis’. Often times the substances whose concentration it is desiredto measure are present in a matrix of other substances. Sometimes thismatrix is quite large and complex. In this case it may be difficult toseparate analytically the target substances from extraneous or perhapseven interfering substances. In all cases, those substances whoseconcentrations are desired of measurement are commonly called analytes.This definition is adopted for purposes of this patent application.Quite frequently the specific concentration of individual analytes needsto be measured. For instance, determining the concentration of ethane inthe presence of ethane and ethyne.

Often individual analytes can be specifically identified by separatingthem from other analytes on a chromatographic column, or by causing themto absorb measurable quantities of light at a specific wavelength notabsorbed by other analytes, etc. In other circumstances it is sufficientto measure the concentration of generic classes of analytes, such asmethane (a specific chemical entity) and nonmethane (a potentially hugearray of many 10's or 100's of individual) hydrocarbons often measuredin the atmosphere or in auto exhaust. Analytical chemists often use theword determine to indicate the measurement of the specific concentration(such as in moles/liter, grams/liter, ug/m3, molecules/cc etc.) of anindividual analyte. On the other hand, the word detect may mean to sensethe presence but not the actual concentration of a specific analyte.Such common definitions are adopted for the purposes of this patentapplication. If an analyte cannot be sensed at all in a sample it istermed to be below the detection limit. This minimum is also referred toas the limit of detection LOD. In this case Pneumatic Focusing may beemployed to make it detectable and to enable its determination. Often inanalytical chemistry, theoretical equations are employed in suchdeterminations, and often various types of standards are employed aswell. These standards may be either internal (present naturally or byaddition to the sample) or external (delivered to the analytical deviceseparately from the sample).

II. Chromatography Types/Terms

1. Packed Column Gas chromatography refers to chromatography carried outwith a packed metal, glass, or other column, typically ⅛″ or ¼″ indiameter. Head pressures are typically 30-60 psi and no flow restrictionis used downstream from the column. A wide variety of commercial packingmaterials are used. Lengths are variable. Flow rates are typically 20-40milliliters/minute. The use of such columns has declined with the adventof capillary column chromatography, but these are still commerciallyavailable, or can be packed in-house with commercially purchased packingmaterials.

2. Capillary Column Gas Chromatography uses longer, open tubularcolumns, the inside walls of which are coated with some type ofadsorbent or absorbent material. Lengths are typically from 30-105meters. Inside diameters typically range from 0.18 mm to 0.53 mm. Flowrates are typically 1-2 milliliters/minute, with head pressures of 30-60psi. Makeup gas often is used with these columns to increase the flowrate into (for instance) a FID detector. These columns are availablecommercially.

3. Packed Capillary Column Gas Chromatography uses narrow-bore capillarycolumns, which are packed with very small beads of varying composition.A recent innovation, these are often packed in-house with commerciallypurchased materials. Since these columns are very narrow and packedtightly, high head pressures are necessary to achieve adequate flows.This is sometimes termed High Pressure Gas Chromatography (HPGC).

4. Supercritical Fluid Chromatography (SFC), is similar to packed columnor capillary column gas chromatography, except that the eluent is oftenCO2 at high enough pressure that it is a supercritical fluid. As such ithas higher solution powers than a gas, but retains some of the gasphase's high diffusivity, which aids separations. By definition, thecarrier is at high pressure to achieve supercritical fluidity. This isaccomplished by a flow restrictor at the column end, either before orafter the detector depending upon the application. Because of the flowrestrictor at the end, the gas expands to atmospheric pressure, yieldinga large volume flow rate under standard conditions. When first developedSFC was termed dense gas chromatography (e.g. J C Giddings, M N Myersand J W King, “Dense gas chromatography at pressures to 2000atmospheres,” Journal of Chromatographic Science 7 (1969) pp. 276-283.In some respects this chromatography is similar to liquidchromatography. R M Smith has reviewed the current status of SFC in thepaper “Supercritical fluids in separation science—the dreams, thereality and the future” Journal of Chromatography A 856 (1999) pp.83-115.

5. Solvating Gas Chromatography (SGC), in which there is no flowrestrictor at the column end but the upstream head pressure is highenough to generate a supercritical eluent for part of the length of thecolumn. At some point the pressure drops enough that the eluent (oftenCO2) changes from a supercritical fluid to a gas. See for instance YShen and M L. Lee “High speed solvating gas chromatography using packedcapillaries containing sub-5 um particles,” Journal of Chromatography A,778(1997) pp. 31-42,

6. Liquid Chromatography (LC), which uses narrow bore or packed columnsand liquid eluent(s). High pressures are required to force the liquideluent through the column because of the higher viscosity of the liquidphase. Hence this is sometimes called high-pressure liquidchromatography (HPLC). Often two different eluents are graduallyinterchanged during the chromatogram (for instance from a less polar toa more polar eluent) in what is termed gradient elution.

Summary of High Pressure in Chromatography

High pressure in chromatography today is typically employed for one oftwo reasons:

-   -   1. is required so that the carrier fluid will pass through a        separatory column in an acceptable length of time. (HPLC, HPGC)    -   2. is employed because of the enhanced solution capabilities of        fluids at high pressure and also because of their ability in        some cases to displace analytes from the separatory column,        thereby enhancing movement of analytes which strongly adsorb to        the column material. (SFC, SGC)

It is current wisdom that the high pressure required to force the liquidcarrier through tightly packed particles in chromatography is anunavoidable evil associated with the high resolution which tightlypacked particles generates. To quote Yufeng Shen and Milton L. Lee inthe paper “High speed solvating gas chromatography using packedcapillaries containing sub-5 um particles,” Journal of Chromatography A,778(1997) pp. 31-42, the main practical problem resulting from the useof small particles in LC is the large pressure drop along the column,which imposes special requirements on the LC instrumentation to handlehigh pressures. In supercritical fluid chromatography (SFC), the effectof the pressure drop on chromatographic performance is relativelycomplex [15-18] and affects both column efficiency and retention ofsolutes. The use of microparticles and the resultant high pressures inpacked column GC (i.e SGC) introduces a practical difficulty in sampleintroduction. However, the well developed sample injection valves withsmall sample loops used in LC and SFC can minimize this problem (citingD. Tong, A M Barnes, K D Bartle, A A Clifford, J Microcol. Sep. 8 (1996)pp353-359). These authors recommend injection of small sample volumesbecause of the high pressure associated with HPLC, SFC or SGC. Thus thecurrent wisdom is to consider high column pressures an undesirable butunavoidable consequence of tightly packed column materials which areuseful for the high resolution they enable. Likewise, V Jain and J BPhillips in the Journal of Chromatographic Science 33 (1995) pp. 601-605state The use of low sample capacity narrow-bore capillary columns putsgreat demands on sample introduction and detection. As the internaldiameter of the column decreases, the maximum sample volume also dropsrapidly. This small volume is hard to manipulate and often causesproblems in column performance with small diameter capillary columns.Thus common perception in the field is that large samples are to beavoided. Such wisdom is certainly not correct in trace analysis,especially automated trace analysis.

In contrast to this conventional wisdom, Pneumatic Focusing allows verylarge samples to be introduced to a capillary column, and in workingembodiments narrower columns produced better peak resolution than widercolumns coated with the same material (e.g. alumina) even when verylarge samples were introduced. It appears that current wisdom hasmisjudged the usefulness of high pressure (Pneumatic Focusing) both inchromatography and in spectrometry. This is due, at least in part, tomuch the work in the art NOT being applied to trace level determinationsand especially not to automated trace analysis. If adequate analyteconcentrations are present in the sample, then Pneumatic Focusing willbe less useful. Even then, however, it may allow better separation ofcomplex mixtures into individual compounds (analytes) for instance suchas in chromatography by reducing injection volumes and limitinginjection band broadening.

III. Spectroscopy Types/Terms

Spectrometric measurements are normally interpreted in terms of theBeer-Lambert Law I=Ioe−a c l or alternately I=Io10−a c l where a is theabsorption coefficient, c is the absorber's concentration and l is thepath length. Using this law, previously measured and recorded absorptioncoefficients, a measured path length, and an experimentally measuredabsorbance Io/I, the concentration c of an analyte can be determined.Thus absorption responds to the product of concentration and pathlength. If an analyte is present at low concentration, especially in theatmosphere, sensitivity can be increased by using a long path length.This is especially important in gas phase measurements, especially inthe atmosphere where it is important to determine the concentrations ofvery trace components. These concepts apply to measurements made at anywavelength, for instance microwave, IR, VIS, UV, etc. Theseconsiderations apply to many types of spectroscopy, includingDifferential Optical Absorbency Spectroscopy (DOAS), Fourier TransformInfrared Spectroscopy (FTIR) NOIR and other derivative andnon-derivative measurements. Long path lengths are used in several ways:

-   -   1. A long physical path length is used. For instance a light        beam, including a laser beam, may be propagated to a detector        meters or even kilometers distant.    -   2. Similar to 1, but a reflector is used at a distance to        reflect the beam back to a detector co-located with the beam        source.    -   3. A folded path is used. In this application, such as in a        White Cell, two mirrors are used to reflect a beam over a base        path a number of times, thereby increasing the total path        length. The number of reflections and the base path length        (distance between the mirrors) is variable.    -   4. A waveguide is used to confine the light beam. In situations        where a sample is contained in a tubular material with        refractive index lower than the sample itself, complete internal        refraction occurs and the beam may be effectively propagated        over long distances to a detector. Recently, new Teflon        formulations have been developed with refractive indices less        than that of water and thereby form effective waveguides for        absorption in aqueous samples. Metals, with real refractive        indices <1 are potentially useful waveguides.

An important property of gas phase spectroscopy or spectrometry is aphenomenon known as pressure broadening wherein the height to widthratio of an absorption feature decreases with increasing total gaspressure. This broadening is caused by interactions between the analytemolecules and any other gas phase molecules present. Further, althoughBeer's Law is know to hold over a wide range of conditions, it is by nomeans followed under all conditions of pressure, concentration orintensity of the probe light source.

Although the concentration dependence of Beer's Law is well known, thecurrent spectrometric art does not teach or suggest high samplepressures i.e. it does not teach or suggest Pneumatic Focusing traceanalysis.

Summary of Pressurization in Absorption Spectroscopy

It is not recognized in the current art that for trace gas analysis,Pneumatic Focusing trace analysis of a sample will result in greaterdetectability. U.S. Pat. No. 4,749,276 describes a long path absorptioncell whose prime novelty involves heating to prevent condensation ofcondensable vapors. This patent does refer to the cell being sealed soit can operate above atmospheric pressure. This patent states that:

It is an object of applicants' invention to produce a White-type cell,which can function to measure condensable gases at elevated pressure.

Note the use of the qualifier “condensable gas”. It appears that theauthors didn't consider the very high pressures of Pneumatic Focusingtrace analysis, or that this method would be useful in the measurementof gases which would never condense even when compressed. That is, gasesat such low partial pressure/concentration that their vapor pressurewould not be exceeded even with very high pressurization. It appearsthat these authors did not envision Pneumatic Focusing as they fail todiscuss precautions that must be taken to ensure that the cell does notexplode when subjected to high pressures. Rather, they simply discuss‘sealing’ the cell, providing no information of how high a pressure thiscell could take or of any of the benefits or disadvantages of going tovery high pressure. Further, as shown above, in Pneumatic Focusing traceanalysis it would be advantageous to first pressurize the sample gasbefore introducing it into the long path absorption cell so that much ofthe IR absorbing water would be removed outside of the cell. This isimportant because water is opaque in many regions of the IR. If a samplecontaining water vapor was introduced into the above cell and thengreatly pressurized, water would condense on whatever components wereheated the least. If the temperature was so high as to completelyprevent condensation, then water absorption of the IR beam would occur.If the temperature were not high enough to prevent water condensationthen the cell could be damaged or corroded by the liquid water.

Spectrometric Effects of Pneumatic Focusing

Pneumatic Focusing trace analysis may be used either to replace orcomplement such path length absorption processes. Whereas an increase inpath length can produce increased absorption and increased sensitivity,an increase in concentration through pressurization or PneumaticFocusing can do the same. Such pressurization may be carried using ahigh pressure driving gas, such as in the exemplary chromatographictechnology described here, or by means of a piston, compressor or othersuch device. Long path lengths, especially reflected paths, may be usedin combination with Pneumatic Focusing. Waveguides will be useful withPneumatic Focusing as the sample can be compressed to high pressures,generating a higher refractive index for the sample so that itsrefractive index became higher than that of the containment vessel,enabling complete internal reflection of a probe light beam. Can cool toenhance compression i.e., liquefy the sample.

Spectroscopic Details of Pneumatic Focusing

When air or other sample gases are compressed to higher pressurespotential analytes are increased in concentration and condensables areseparated so that both (if desired) can be subjected to separateanalysis. In addition, any reactions which may be occurring within thegas sample are accelerated, since reaction rates are proportional to theproduct of the reactants' concentrations.

As an example, ozone reacts with alkenes in ambient air. If such air ispressurized, for instance by a factor of 10, these reactions will occurfaster, in this case by a factor of 100. However, the rate of fractionalalkene removal by the reactive ozone will be increased only by a factorof 10. Thus is it already known within the field of atmosphericmeasurements to remove ozone from a gas sample before either storing itfor later analysis, or passing in into any sort of collection offocusing device. This standard technology may be applied to PneumaticFocusing as well. Standard methods of ozone removal include reactionwith added nitric oxide NO, or removal on some surface, such as a coppersurface, or a glass fiber surface which has been coated with reactivepotassium iodide.

Other pitfalls to be recognized or avoided in Pneumatic Focusingspectrometry include:

-   -   1. Absorbance commonly increases linearly with pressure due to        increasing concentration as expected from Beer's Law, but this        is not always the case.    -   2. Absorbance can increase proportional to the square root of        the pressure ratio due to dimerization of the target analyte to        produce a nonabsorbing dimer.    -   3. Absorbance can increase proportional to the square of the        pressure ratio, which without limiting any invention to a theory        of operation, may be due to absorption of dimers or collision        complexes.    -   4. Absorbance can increase and remain constant due to        condensation of the target analyte to a liquid which is removed        from the view of the absorbed light beam.    -   5. Absorbance may increase, decrease, or otherwise behave        erratically.    -   6. Broadening of the absorption lines can occur.    -   7. Interference from unwanted spectral bands of the sample (e.g.        O4 absorptions) not present at the original sample pressure and        whose intensity is dependent upon the focusing pressure can        occur.    -   8. Transmitted light intensities can oscillate, perhaps        randomly, indefinitely in time, but time averaging can be used        to determine absorbances and concentrations.

II. Apparatus

FIG. 1 is a schematic of a working embodiment of a system useful forpneumatically focusing, and analyzing a gaseous sample using a gaschromatograph. The components of the system, and their connections, willbe discussed with reference to FIG. 1. A more detailed description ofcertain components of the system also is provided.

FIG. 1 illustrates a chromatographic system 10. A working embodiment ofsystem 10 as illustrated in FIG. 1 has been used for continuous, realtime monitoring of ambient air. This system 10 has operated almostcontinuously for more than one year sampling ambient air for a totalof >10,000 samples on the same alumina column. A sample line 12 havingan outdoor sample inlet 14 was used to collect ambient air outside of abuilding. For this illustrated embodiment, the sample line was made ofTEFLON, and was approximately 30 meters in length. A person of ordinaryskill in the art will recognize that the sample line can be made fromother materials, such as other plastic materials or metals, such ascopper tubing. The length of the sample line is determined byapplication, and is not critical to the operation of the present system.

In this application a virtually instantaneous sample was taken. Suchsample is most suitable for determining emission source distributions(which information is degraded by averaging over large sample volumeswhich have been impacted by varying sources). It is more common in thefield of air sampling to use integrated samples. For instance, a gascanister is slowly filled over a period of 1, 2, 24, etc. hours and thentransported for laboratory analysis. Or, air is passed slowly through anadsorbent cartridge for 1, 2, 24, etc. hours. In some applications thistype of sampling might be preferred with PFGC. Time averaged samplingmay be accomplished several ways (without limitation) using PFGC. Forpurposes of these examples, assume the sample analysis time to be 40minutes.

1. Sample on an instantaneous time basis and then average individualchromatograms together before analysis. This yields a bettersignal-to-noise ratio and hence sensitivity or detection limit asdiscussed elsewhere than analyzing a single accumulated sample a singletime. For instance 40 samples taken on a 40 minute basis may be averagedto compare with a single 24-hour integrated sample.

2. Sample on an instantaneous time basis but draw the air samplecontinuously into a collection/averaging volume during the 40 minuteanalysis time. If the sample rate were 10 cc/min and the averagingvolume were 400 cc then the averaging time would be 40 minutes. Thuseach 40 minute sample would be an average over that time period ratherthan an instantaneous sample taken every 40 minutes.

3. As in 2 but choose an integration averaging time (=volume/flow rate)of any desired time.

Sample line 12 was fluidly connected via a multiport sampling valve 16to a sampling pump 18. Sampling pump 18 is used to, if desired,continuously draw gaseous samples, such as ambient air samples, into thesampling line 12. Further fluidly connected to the sampling valve 16 isa carrier gas inlet line 20, a sample loop 22 and a separatory column24. Carrier gas inlet line 20 is fluidly connected to a carrier gassource, such as the carrier gas cylinder 26. In a working embodiment,the carrier gas was helium. Typically, a high-pressure regulator 28 iscoupled to the carrier gas source for regulating the pressure deliveredto the system by the carrier gas. Additionally, a VOC adsorbing filter,not illustrated but described elsewhere, was fluidly coupled inlinebetween the high-pressure regulator and the multiport valve. A workingembodiment used an activated carbon filter to remove VOCs and otherimpurities from the carrier gas so that they do not appear as spuriouspeaks in the chromatograms. This allowed lower grade and cheaper carriergases, for instance ‘balloon grade’ helium, to be used. Since thesefilters can themselves restrict flow and cause pressure drop to thepneumatic chamber, a pressure gauge may be placed between the filter andthe multiport valve so that pressures may be adjusted correctlyindependent of the regulator gauge and so that gradual clogging of thefilter may be monitored.

Sample loop 22 is fluidly connected to two ports of the multiportsampling valve 16. The carrier gas is connected to the sampling valve 16by carrier gas inlet line 20, which is fluidly connected to a first portof the valve 16. Separatory column 24 is fluidly connected to a port ofthe valve 16. The illustrated embodiment of the valve 16 had only twoprimary positions, a sampling position and an injection position. In thesampling position, sampling pump 18 continuously draws air through thesample line 12 and through the sample coil, while carrier gas from gassource 26 is delivered to valve 16 by sample line 20. In the samplingmode, carrier gas passes through the valve 16 and through the separatorycolumn 24. In an injection position, valve 16 allows carrier gas to passthrough sample loop 22. The carrier gas pushes the gas sample collectedin the sample loop ahead of it, thereby pneumatically focusing thegaseous sample, and into the separatory column 24. Valve 16 can bemanually operated, but preferably is operated by a control computer sothat the sampling and analysis conducted by the system can be automated.

Downstream of the column 24 is a pressure increasing/flow reducing valve30. Actuating valve 30 increases fluid pressure in the line and reducesfluid linear velocity through the line. Thus, once a gaseous sample ispushed towards the column 24 by a carrier gas, the gas sample iscompressed to a second smaller volume, and therefore analytes in the gasare concentrated. The pressure of the line can be maintained as, andsubsequent to, the gaseous sample being injected onto the GC column.Compressing the gas sample can be used to condense certain materials,such as water, in the gaseous sample before the sample is injected ontothe column. One important benefit of this system is that water condensedby Pneumatic Focusing can be condensed prior to entering the column andhence mostly prevented from entering the column. For instance,isothermally compressing the sample gas initially at 100% RH from 15 psi(atmospheric) to 300 psi (pneumatically focused) would condense 1-15/300or 95% of the water. By appropriate valve switching, the vast majorityof the sample water vapor would not enter the column or other analyticalfashion. This illustrates the nonobvious design of Pneumatic Focusing.

Alternately, if it is desired to inject the gaseous and condensed waterwith the sample this may be accomplished several ways, such as:

-   -   1. The sample compression section may be heated sufficiently        that water will not condense even at high pressures.        Thermodynamic calculations or empirical tests can determine the        appropriate temperature.    -   2. The carrier gas may continue to pass through the sample        compression section long enough to reevaporate condensed water        and other condensables and sweep them onto the head of the        column.    -   3. 1 and 2 may be used in combination.

Alternately, the condensed water and any dissolved components may becollected through a separate port and subjected to additional chemicalanalysis either by direct spectroscopy, pH determination, or othermeasurement such as by additional chromatographic separation andanalysis.

Column 24 is fluidly connected by sample conduit 32 to a detector, suchas a FID detector, 34. Thus, gaseous sample that has been pneumaticallyfocused and injected on the column 24 is diverted through detector 34.Plural detectors (not illustrated), either connected in series or inparallel, also can be used. If connected in series, then detectors thatdestroy the sample, such as a flame ionization detector (FID), should belast in the series. If detectors 34 are connected in parallel, thenportions of the gaseous sample from column 24 are diverted, as desired,into such detectors.

FIG. 1 illustrates a system that utilized an FID 34. FID 34 was usedbecause one primary use for the illustrated system, without limitation,is continuous sampling of VOCs in ambient air and in human breath. FIDsare especially well suited for detecting the minute quantities of VOCsin pneumatically focused samples produced. FIDs require both a fuelsource and an oxidizer source. FIG. 1 illustrates fluidly connecting FID34 to both a hydrogen (fuel) cylinder 36, via supply line 38, and to anoxidizer (oxygen) cylinder 40, via an oxidizer supply line 42. Both fuelcylinder 36 and oxidizer cylinder 40 include conventional pressureregulators 44 and 46, respectively.

Gaseous samples pneumatically focused are analyzed by desired chemicalanalysis instruments, such as the gas chromatograph 48 (e.g., a Varian3400 gas chromatograph) illustrated in FIG. 1. The Varian 3400 gaschromatograph used in one working embodiment of the present system alsoincluded a keypad 50. An operator using the keypad enteredchromatographic processing parameters into the chromatograph.

The entire operation of the present system was automated, and theworking embodiment of the present system as illustrated in FIG. 1 wascomputer controlled. Computer 52, such as a 486 personal computer, waselectrically coupled to the detector 34. Signals generated by thedetector 34 were routed to computer 52 through an amplifier A/Dconverter 54. Computer programs, discussed below (source codes for whichare attached hereto as an appendix) controlled the operation of thecomputer to determine when samples were collected and analyzed. As withany computer, input to computer 52 can be accomplished as desired, suchas through a keyboard 56. Data generated/analyzed by the computer can bedisplayed, if desired, on a computer monitor 58. These data could besubjected to real-time, digital signal processing to reduce noise andimprove signal to noise ratio. Such data, as well, could be subjected toreal-time peak integration for direct reporting of analyteconcentrations. Also, the computer 52 can be linked via a modem to aremote operating station, or can download data to an internetconnection, if desired.

Certain of the components described above with reference to a workingsystem will now be described in more detail. The system was made bymodifying commercially available chromatographs, such as Varian 3000series chromatographs. Models No. 3400 and 3700 were used to construct 2working embodiments. However, virtually all known chromatographs can bemodified to be useful for Pneumatically Focusing gas samples.

A person of ordinary skill in the art will recognize that workinginstruments could include elements in addition to those described below.Moreover, a person of ordinary skill in the art will recognize that theelements listed below could be modified from that described to include,for example, future-developed features. Further it should be realizedthat a more suitable, more saleable, more compact, etc., instrumentcould be designed, constructed, and built from scratch.

1. Compressed Gases/Delivery Cylinders

Compressed gases are used for a number of purposes, such as (a) toprovide a carrier gas that carries the sample through a separatorycolumn and/or (b) to provide a gas that fuels the flame, the electricalconductivity of which forms the basis for detecting analytes using flameionization detection of individual, separated VOCs.

The carrier gas can be any gas deemed suitable for carrying samplesthrough a separatory column. Working embodiments of the presentapparatus have used helium (He) as the carrier gas. A number of othersuitable and useful carrier gases can be used, depending upon thedetails of the application, including hydrogen (H2), nitrogen (N2),argon (Ar), carbon dioxide (CO2), ambient air, or any of a multitude ofother gases, including gases doped with suitable internal standards. Inone application, the carrier gas (e.g. CO2) may be compressedsufficiently to generate a supercritical fluid.

Suitable carrier gases may be used singly or in combination. Moreover,plural gases can be used in various combinations during the course ofPneumatically Focusing or analyzing samples. For example, thechromatogram initially could be generated using Pneumatic Focusing andinitial column separation using helium. At some point, the carrier couldeither continuously or discontinuously, be changed from helium to, forexample, supercritical fluid carbon dioxide. By this method, a carriergas of varying composition over time could be developed. Changing thecarrier gas in PFGC gradually from helium to supercritical carbondioxide would allow eluting from the column those analytes which heliumis not capable of eluting. This gradient elution could thereby allow anautomated chromatograph to operate using a constant oven temperature.This allows considerable savings in complexity and electrical power fora remotely operating instrument. In this case, analyte separation andelution would be accomplished by a combination of factors, such ascarrier gas composition, pressure, and flow rate, includingsupercritical fluidity of the carrier for part or all of thechromatogram. Another such approach would be to employ a liquidchromatograph. Chromatographic carrier gases can be contained atelevated pressures (1000-10000 psi) in compressed gas cylinders. InPneumatic Focusing these compressed gases can serve to compress thepneumatically focused sample in the sample loop and into thechromatographic column. This could also be accomplished with a minimumof diffusional mixing between sample and Pneumatic Focusing/carrier gasthrough the use of a pneumatic piston described herein separately.Following delivery to the chromatographic column, each VOC componentseparated by the separatory column is consecutively eluted into a FID.

FIG. 2 illustrates a Pneumatic Focusing Spectrometric System 60 (PFSS).Components of this system were selected to withstand pressures of 15 to2,500 psi as delivered by a compressed nitrogen cylinder. This systemconsists of a metal or glass light absorption cell 62 fluidly connectedwith Swagelok fittings and 3-way valves 64 and 80 to a sample containingloop (200′ coil of ¼″ od copper tubing) 66, a sample providing pump 68,a compressed nitrogen cylinder 70 and high pressure regulator 72 todeliver the Pneumatic Focusing pressure. Gas from cylinder 70 isdelivered via a fluid conduit 74, through a 2-way valve 76 and pressuregauge 78. Gas from cylinder 70 is then routed via Whitey 3-way valve 80to cell 62. Spectrometric measurements were provided by an Ocean OpticsPC-2000 spectrometer (not illustrated) which consisted of a diode arraycard located inside a personal computer 83 running Windows98. Light tothe cell 62 was provided by an Ocean Optics mini-FT2 combined UV-VISlight source 84 providing light from approximately 200 to 900 nm. Lightwas passed through the cell 62 using end windows consisting ofUV-transparent fused silica lenses 80 a, 80 b from Edmund Optics#K45-693. Light was conveyed from the cell 62 to the diode array cardwithin the computer 83 by an optical fiber 82 included with the PC-2000.

In a working embodiment, the valves, such as valves 64, 76 and 80, wereoperated manually. These valves could in continuous operation beoperated by personal computer 82 containing the spectrometer.

One method (without limitation) for operating this Pneumatic Focusingspectrometric system PFSS is as follows:

1. The system 60 is assembled as illustrated in FIG. 2. All componentsdescribed herein have withstood 2,000 psi focusing pressure, butappropriate precautions should always be taken in assembling such asystem. This system was pressurized for the first week by an operatorstanding behind a ¼″ section of safety glass. In FIG. 2 pressure gauge78 allows the Pneumatic Focusing pressure to be determined. Typicaloperation (without limitation) is as follows.

2. A sample 13 drawn through ¼″ Teflon tubing 90 leading from the sampleinlet 92. In this set of tests various test gases contained in plasticbags were delivered to the PFSS at port 92.

3. Before initiation of spectrometric measurements, appropriatemeasurements of lamp and dark intensities are made. Such operations,familiar to practitioners of the spectrometric arts, are described inthe Ocean Optics manual. Initially, the spectrometer is placed in‘Scope’ mode and the lamp intensity (Io) is recorded and saved incomputer memory. Since data at each wavelength are recorded with a12-bit A/D board, the sampling time should be set such thatapproximately 3500 counts are displayed on the computer screen at themaximum point in the intensity curve. Any desired spectral averagingnumber may be selected as well. For many applications no averaging isrequired and the computer will update absorbance measurements every fewseconds or so. Next, the optical fiber 82 is removed from thespectrometer cell 62 and light is blocked from entering it, such as bythe operator's thumb. Under computer operation the operator's thumbwould be replaced by a computer actuated shutter between the fiber 82and the cell 62. This dark current is recorded and stored in computermemory. This forms Idark as is commonly employed in spectrometry, theconcentration of an absorber is given by solving the equation:A=log((I _(o) −I _(dark))/(I−I _(dark)))=ac1

Thus absorber concentration is proportional to A which is computedautomatically and displayed by the computer as a function of wavelength,in real time, on the computer screen. After these initial measurementsthe program is placed in absorbance mode.

1. With valves 64, 80 and 2-way valve 94 in the appropriate position,pump 68 draws air from a source through sample coil 66 and throughspectrometric cell 62. Care should be taken that the entire sample coil66 and cell 62 are filled by such sample. Since sample arrives at thespectrometer cell 62 last, this may be ascertained by observing thelight absorption spectrum on the PC computer screen. In the case whereno discernable absorption is present before Pneumatic Focusing asufficient length of time should be allowed for sample to arrive.

1. When sample delivery is complete the initial absorbance may berecorded and saved to computer memory.

2. Valve 94 is thrown to the opposite closed position to isolate pump 68from the system.

3. The sample is pneumatically focused to the desired pressure. This maybe carried out without limitation as follows. The pressure regulator 72is set for a pressure less than or equal to the starting, atmosphericpressure. Valve 64 is moved to the opposite position, fluidly connectingtank 70 through regulator 72 to sample coil 66, valve 80 and cell 62(valve 76 remains closed). Then regulator 78 is slowly adjusted upwardin pressure, allowing nitrogen pressure to build up in the sample loopand spectrometric cell 62, pneumatically focusing the sample containedtherein. Absorption may be observed on the computer screen continuouslyduring this process. When the system 60 has reached equilibrium (a fewseconds, assuming pressure was increased gradually) the absorbancespectrum is recorded and saved to computer memory. In the process ofsample focusing within the sample loop 66, condensed water will beformed, and if the process occurs slowly (as is advised for the purposesof these measurements), most will be removed on the walls of the sampleloop 66 rather than enter the sample cell 62.

4. This process is repeated to produce a series of recorded spectra atvarious focusing pressures such as discussed in one of the examplesbelow.

5. To terminate the process, regulator 72 is adjusted back to pressureless than 1 atmosphere, and pressure is bled from the system 60 byslowly opening either valve 64 or valve 94. In manual operation pump 68may be removed before pressure is bled off to avoid displacing therubber diaphragm inside the pump (this diaphragm is easily replaced).Alternately, check valves and bleed valves, such as illustrated in FIG.3 and FIG. 4 may be bleed check valve employed.

6. If pressure is bled off slowly through valve 64 and no irreversiblechemical reactions have occurred at focusing pressures, the spectrashould retrace the results obtained during pressurization

7. If pressure is bled off through valve 94 the spectrometer shouldquickly return to a ‘zero absorbance’ reading as the non-absorbing,focusing nitrogen gas enters the spectrometric cell.

The PFSS illustrated in FIG. 2 can perform another function through theuse of valve 76. In this operation compressed gas cylinder 70 isconnected directly to cell 62 without passing through the sample loop66. In this way the effect of pressure (pressure broadening) on anydesired analyte may be determined with said analyte remaining atconstant concentration. In this operation the analyte is first drawnthrough the sample chamber 62 as above. Once a stable absorptionspectrum is obtained, valves 64, 94, 80 and 76 are reversed therebyconnecting cylinder 70 through regulator 72 to sample chamber 62. Thuspressure administered from the compressed gas cylinder 70 serves toincrease the pressure to which an analyte is exposed while maintainingconstant analyte concentration. When carrying out these measurementssufficient time should be allowed for the analyte to diffuse into newlyadministered pressurization gas.

For samples containing water vapor, such as ambient air samples,focusing as described above will condense water vapor onto the walls ofthe sample coil 66. If removal in this manner is insufficient, a filter(not illustrated) may be included between the sample loop 66 and thecell 62. One caveat in water condensation is partitioning of watersoluble analytes into the condensed water vapor. This process isdescribed by Henry's Law.

An exemplary calculation of the nature of this affect is given here foracetone. The NIST web site (http://webbook.nist.gov/chemistry/) liststhe Henry's Law coefficient for acetone solubility in water as kH=30mole/(kg*bar)˜30 (mole/kg H₂O)/atm.

Consider 1 liter of ambient air that has 1% water vapor by volume.(Saturation at STP is about 3% so this is about 33% RH). Pressurizationto 100 atmosphere would condense virtually all the water vapor. UsingPV=nRT, this would produce:n=0.01 atm*1 L/(0.082 L-atm/K-mole*298K)=4.1 e−4 mole H2O4.1 e−4 mole*18 g/mole=7.4 e−3 g H2O=7.4 e−3 ml=7.4 uL H2O=7.4 e−6 kgH2O

Assuming 1 ppb=1 e−9 atm of acetone compressed to 100 atm in the samplewe haven=1 e−9 atm*1 L/(0.082 L-atm/K-mole*298K)=4.1 e−11 mole acetoneKH=30(mole/kg H2O)/atm*7.4 e−6 kg H₂O*1 e−7 atm Acetone=2.2 e−11 moleacetone.

Thus acetone would partition into the condensed phase about 1 liquid:2gas at a Pneumatic Focusing pressure of 100 atm=1500 psi. The fractionpartitioned would be negligible at 10 atm or 150 psi.

Benzene is much less soluble in water than acetone with KH=0.16. Thusbenzene partitioning into water would be negligible even at 100 atm.

These calculations, based upon proportions, are independent of thevolume of air pneumatically focused.

Pneumatic Focusing Spectrometry consumes significant quantities of thepressurization gas for a sample loop of 1 L volume. A more attractiveapproach (also applicable to PFGC) is to use without limitation any of avariety of piston-type devices. Four such embodiments have beendeveloped or envisioned to date.

1. One such device was constructed using a piston/cylinder and a 12Velectronic trailer jack (Atwood company) to provide the compressionforce. In a laboratory model, the jack was attached to a cast iron mountwith stainless steel hose clamps. The cylinder, which contained ano-ring-sealed piston, was similarly attached. Application of 12V to thejack actuated piston, driving the contained air sample into either aspectrometric sample cell or onto the head of a GC column. In thisfashion pressure was increased by the application of voltage to thepressure jack. Higher pressures could be generated using a longerpiston.

2. A hydraulic cylinder of about 10 liters volume is compressed by avariable speed high torque motor. This large device would easily deliversufficient sample for a spectrometric cell but would be larger thannormally required for PFGC.

3. Another such device 100 (FIG. 6) employed a 12V (cigarette-lighterplug in type) compressor designed for inflating tires. This miniaturecompressor was equipped with coiled copper tubing 102 having inlet 104through which cooling water flowed to prevent overheating. Tubing 102also included an outlet 106. The compressor included a motor 108 and agearing device 110. Motor 108 actuates piston 112 into reciprocatingmotion within cylinder 114. Cylinder 114 has a delivery conduit 116having a gas flow outlet 118 and a liquid flow outlet 120. A flowregulating material, such as a glass wool plug 122, also can be usedwithin conduit 116. Pressure is measured with gauge 124. The compressorwas connected to a spectrometric cell through a section of Teflontubing. A downstream valve below the spectrometric cell regulated flowrate through and pressure within the cell. With this device it waspossible to feed a continuous air sample for spectrometric analysis tothe cell at pressures ranging from 60 to 120 psi. Such tire pump, notbeing designed for continuous operation, could be replaced by a moresuitable small compressor in actual practice and would deliver a higherPneumatic Focusing pressure. Otherwise, such compressor could be used todeliver periodic samples by computer control to a chromatographicdevice. Since Pneumatic Focusing results in conversion of condensablegases (e.g. water) to liquids, it is possible to separate said condensedliquids from the non-condensed pneumatically focused air stream. Each ofthese two pneumatically focused samples could be directed to anappropriate detection device. For instance (without limitation) theliquid sample could sent to a liquid chromatograph and the gas sample toa gas chromatography alternately, both could be sent to different gaschromatographs, or to different columns in the same gas chromatograph.The aqueous fraction may be subjected to a variety of nondestructivemicro determinations such as pH or specific ion electrode measurements.Persons familiar with the art will appreciate the extremely wide rangeof analytical possibilities for these two sample streams.

4. Another such prototype application would employ the small compressoras the continuous gas feed (carrier gas) to a chromatographic system.Since the compressor delivers ambient air, any compounds present inambient air which collect on the head of the column would elute and formpeaks during temperature programming of the column. Thus air could formboth the analyte and the carrier gas.

2. Sample Collection Tubes

A gas sample is collected so that it can be pneumatically focused andinjected onto a separatory column of a GC. This has been accomplishedusing coiled collection tubes typically made out of metal, such ascopper. Copper has the advantage of catalytically destroying ozone whichmay be present in ambient air samples and which could remove alkene VOCsduring Pneumatic Focusing (see above). Working embodiments have used oneor more sample collection tubes connected in parallel for collectingsamples. The collection tubes typically have been about ⅛ inch exteriordiameter copper tubing approximately 50 feet in length. By increasingthe length of the collection coil, or by coupling plural collectioncoils together in series or in parallel, a larger gas sample can becollected for injection onto a separatory column of the GC. In otherworking embodiments of Pneumatic Focusing a ¼ inch 50-foot length coilof copper tubing has been using with variable time delay injection undercomputer control. In this fashion the computer may inject from a single0.5-liter sample loop actual volumes ranging from 0.05 liter to 0.5liter. The larger the sample size introduced onto a separatory column,the potentially greater sensitivity that can be achieved. With largersamples higher pneumatically focusing pressures can be used if desiredto maintain sample band width. Variable volume injection may bequantified by any of the internal standard methods described herein.

It will be recognized that injection of larger and larger samples mayproduce some loss in resolution and separation, especially for thosecompounds not collected at the column head.

A multiple injection technique also may be used. In this approach,rather than injecting a single large volume, say 500 cc of sample atonce, the computer is programmed to inject a 50 cc sample 10 times.After each injection the sample pump pulls fresh sample into the sampleloop. After injecting a computer controlled number of times the gaschromatograph is triggered to begin temperature programming. The resultof this multiple injection approach is to generate 10 individuallyresolved methane peaks since methane is not held up by adsorption on thecolumn. There then follows a range of compounds which are not resolvedby the multiple injection technique. Finally individual peaks which wereheld up on the column head by the low initial temperature (in this caseroom temperature) emerge fully resolved and at an intensity 10 timesthat of an individual injection. Under computer control, such multipleinjections could be carried out inversely proportional to theconcentrations of target analytes. For instance, in air monitoring, ifthe air was highly polluted, a relatively small number of multipleinjections could be made. If the air was slightly polluted, a relativelylarger number of multiple injections could be made. The computer coulddetermine pollution levels from each previous chromatogram and adjustthe subsequent number of injections accordingly.

One method which is useful in improving resolution in capillary columnchromatography has been described by Ziment Yan and J G Nikelly inJournal of High Resolution Chromatography 17 (1994) pp. 522-536: “Theuse of precolumns for solvent focusing in capillary column gaschromatography.” Such precolumns also will be useful in improving themanner in which pneumatically focused samples are introduced into acapillary column. This will be particularly but not solely useful infocusing samples which originated as liquid samples but which werevaporized upon introduction into a Pneumatic Focusing gas chromatograph.

Two factors typically are considered when determining the sample sizeand the degree to which the gas sample is pneumatically focused. Thesetwo factors are the sample volume and the compression ratio. Forexample, by both doubling the sample volume and doubling the pressureused to pneumatically focus the sample, to a first order approximationthe result should be substantially the same peak resolution but twicethe sensitivity, since the sample size has doubled, as achieved prior todoubling the sample volume and the focusing pressure. On the other handif the sample volume is doubled, but the focusing pressure is maintainedthe same, then the integrated signal may be increased but the peakresolution and sensitivity may degrade, i.e., the peak width asdisplayed by the chromatogram would increase but not the peak height.Thus, Pneumatic Focusing results in narrower peaks that can be resolvedfrom one another and provides a larger signal relative to instrumentbackground noise. Pneumatic Focusing is enhanced by temperatureprogramming. In previous examples those compounds retained on the columnhead would have enhanced sensitivity when two times the sample size wasinjected at a constant pressure. See example below. There is no clearupper limit to the degree of Pneumatic Focusing in terms of samplevolume, pneumatically focused pressure and resultant sensitivity.Obvious limitations are the pressure limits of those system componentsexposed to the elevated pressures, separation efficiencies on thechromatographic column (if employed), and potential chemical reactionsaccelerated with pressure in the sample. These limits can be ascertainedand perhaps improved by experimentation familiar to persons experiencedin the chromatographic or spectrometric arts.

For air analysis, methane is one VOC that is both quite volatile andrelatively constant in concentration. Other, less volatile VOCs, such asaromatics, tend to absorb, or stick, to the head of the column as thesample containing such materials is introduced onto the column. Theseless volatile VOCs are desorbed from the column by, for example, heatingthe column. Thus, the Pneumatic Focusing of less volatile VOCs may beless important than Pneumatic Focusing of more volatile VOCs. Methane isthe first VOC to emerge from a separatory column due to its relativelyhigh volatility, whereas aromatics such as toluene are, to some degree,additionally focused by their relatively lower volatility and relativelyhigher affinity for the separatory column. The Pneumatic Focusing effectcan be enhanced by selectively cooling a section at the ‘head’ of thecolumn to focus more volatile analytes, using a retention volume, athickly coated precolumn, or any of several other approaches familiar tothose experienced in the art.

In atmospheric analysis it is often desired to measure the methaneconcentration and the sum of all the nonmethane hydrocarbons. U.S. Pat.No. 4,102,648: “Measuring Non-Methane Hydrocarbon Contents in Gases”takes a sample gas which is divided into two portions, one beingsubjected to flame ionization detection to measure all hydrocarbons, theother one being passed through a tube having active carbon to remove allhigher hydrocarbons by adsorption except methane. The resulting gas alsois subjected to flame ionization detection and the difference indetection gives the non-methane impurities, either electrically asdifference signal or graphically. The adsorber tube may be exchanged foranother one while the former is cleaned and purged. A simple flameionization detector is used alternatingly or two are operated inparallel to obtain the two readings. This now standard way to measuremethane and the sum of non-methane HCs would benefit in highersensitivity if adapted for Pneumatic Focusing since a higher signalwould be achieved upon compression, allowing more accurate determinationof the signal difference produced upon removing NMHCs.

Conventional wisdom in the field of air sampling, as discussed in theBackground, is to cryofocus or absorbent focus samples (or both) from afairly large volume to a significantly smaller volume. However, if asufficiently large sample volume is first collected and thereafterinjected onto a separatory column at conventional pressures, such asless than 100 psi, and more typically about 40 psi-60 psi, withoutpneumatically focusing the sample at pressures greater than pressuresused for conventional GC analysis, then the first, most volatilematerials in the sample are not focused, and hence are not resolved.However, VOCs that are less volatile may be resolved by adsorption anddesorption from the separatory column, where desorption occurs as aresult of heating the column. The significant advantage of PneumaticFocusing for less volatile analytes is to pass a large volume of samplegas through the column in the most rapid fashion—which is at highpressure. Thus, even for materials that are primarily focused byabsorption to the head of the column, increasing the pressure at whichsuch samples are driven through the column significantly decreasesprocessing times without sacrificing sensitivity or resolution for thecolumn-focused analytes.

3. Columns

Virtually any known separating column can be used, along or incombination with other columns. Those familiar with the art will realizethat some columns will be more appropriate for individual targetanalytes and that individual columns, coatings or packing materials,etc. may be more suitable than others for PFGC. One working embodimentof the present apparatus used an alumina VOC analysis column,distributed by J&W, (30 m×0.53 mm id) Model No. 115-3532 RT-alumina.This column has passed approximately 20,000 air samples withoutsuffering unacceptable degradation in resolution. A similar Restekcolumn, RT Alumina (60 m×0.32 mm id) Ser. No. 183,143 also was used andgave better resolution than the shorter, wider bore J&W alumina column.Another such working embodiment used a Supelcowax-10 fused silicacapillary column serial #15702-10 (60 m×0.32 mm id×1.0 um filmthickness) for OVOC analysis of ambient air and human breath. Withoutlimitation, other columns that could be used for separating apneumatically focused sample include packed columns, capillary columns,open tubular capillary tube having an interior wall coated with sorbentmaterial, packed capillary column, alumina columns, and combinationsthereof. In other applications, a liquid chromatography or SFC columncould be used.

A portion of the separating column could be further cooled duringseparation of a pneumatically focused sample. The temperature at whichthe cooling would take place could be higher than for cyrofocusing, andinstead such temperatures can be achieved by electrical means withoutusing cryogenic materials, such as liquid oxygen, nitrogen or air. This“reduced temperature” focusing could be used to further focus a sampleat a localized region of a separating column, usually at an upstreamportion thereof, relative to flow of the carrier gas. Thus PneumaticFocusing can obviate the need for cryogenic fluids in gas analysis.Two-dimensional and comprehensive GC, in which successive portions ofthe sample fluid passing through a first column are directed asrefocused pulses into a second column gives significantly higher sampleresolution and separation than a 1-dimensional GC. This technique iscompletely amenable to Pneumatic Focusing of the sample beforeintroduction or during introduction into the first column.

4. Column Packing Materials

Virtually any known column packing material can be used in combinationwith the method of Pneumatic Focusing as described herein. Workingembodiments typically used a column having an alumina absorbent coatedon an inside wall thereof Other packing materials are described inHelmig's Air Analysis by Gas Chromatography, supra.

5. Detectors

A working system used a FID detector. However, persons of skill in theart will realize that Pneumatic Focusing as described herein can be usedwith other detectors. Standard types of chromatographic detectors otherthan FID detectors may be cheaper, more sensitive, or otherwise moreappropriate for a particular application or instrument. Such detectorsmay either operate at the Pneumatic Focusing column pressure, ordownstream of the flow regulating valve at pressures near atmospheric,as is the case for a FID. Descriptions of a selection of suitabledetectors may be found in standard references, such as: “Detectors forGas Chromatography,” Hill and McMinn, John Wiley (1992), incorporatedherein by reference; “Detectors in Gas Chromatography,” Sevcik,Elsevier, (1976), incorporated herein by reference; and others. Inparticular, suitable detectors include, without limitation,photoionization (PID), infrared (IR or FTIR), electron capture (ECD),thermal conductivity (TCD), nitrogen phosphorous (NPD), flamephotometric (FPD), UV/Visible or Raman scattering detectors. The thermalconductivity detector, TCD, is especially simple, inexpensive, and usedwidely. However, many TCDs have limited sensitivity relative to (e.g.)FIDs. Pneumatic Focusing of gaseous samples will greatly extend therange of uses of the TCD and other such detectors for gas analysisbecause of its ability to quickly and inexpensively increase targetanalyte concentrations. It also is possible to use more than onedetector to analyze portions of a pneumatically focused and resolvedsample.

Pneumatic Focusing is especially useful for sample introduction forso-called GC/MS analysis of analytes. In this case, as describedelsewhere herein, column mass flow rate should be decreased afterpneumatic injection by simultaneously dropping column head pressure andopening the downstream valve to allow an increased volumetric flow atthe dropping column pressure.

Some compounds are more appropriately detected by chromatographicdetectors other than the flame ionization detection (FID), or by usingother analytical procedures, such as absorption or fluorescencespectroscopy. The present technology will apply equally as well to mostsuch other gas analysis procedures, and can yield greater sensitivityfor those analytical techniques which respond with greater sensitivityto a compressed sample.

Pneumatic Focusing can be applied to absorption spectroscopy.Spectrometric measurements are normally interpreted in terms of theBeer-Lambert Law I=Io exp(−a c l) where a is the absorption coefficient,c is the absorber's concentration and 1 is the path length. Using thislaw, previously measured and recorded absorption coefficients, ameasured path length, and an experimentally measured absorbancelog(Io/I) the concentration c of an analyte can be determined. Thusabsorption responds to the product of concentration and path length. Ifan analyte is present at low concentration, especially in theatmosphere, sensitivity can be increased by using a long path length.This is especially important in gas phase measurements, especially inthe atmosphere where it is important to determine the concentrations ofvery trace components. These concepts apply to measurements:made-at anywavelength, for instance microwave, IR, VIS, UV, etc. Theseconsiderations apply to many types of spectroscopy, includingDifferential Optical Absorbance Spectroscopy (DOAS), Fourier TransformInfrared Spectroscopy (FTIR), other derivative and non-derivativemeasurements.

Pneumatic Focusing may be used either to replace or complement such pathlength absorption processes. Whereas an increase in path length canproduce increased absorption and increased sensitivity, an increase inconcentration through pressurization or Pneumatic Focusing can do thesame. Such pressurization may be carried out using a high pressuredriving gas, which pushes the sample air into an absorbance chamber,without entering the chamber itself, or by means of a piston, compressoror other such device. Long path lengths, especially reflected paths, maybe used in combination with Pneumatic Focusing.

Waveguide absorption spectroscopy can also be effectively used withPneumatic Focusing.

1. In one embodiment an optical waveguide may be used to measure theabsorption of the water fraction of the sample produced by PneumaticFocusing. Such absorptions would be most easily carried out in the uv orvisible region where water is mostly transparent to the beam radiationso that trace dissolved analytes can be quantitatively determined.

2. In another embodiment the aqueous fraction may be exposed to nonpolaradsorbents coated on the interior surface of the waveguide. Afteranalytes in the aqueous fraction of the Pneumatically Focused sampleadsorb onto the coatings, the water may be removed from the tube byforced air drying and then the concentrations of the adsorbed speciesmeasured by waveguide IR or FTIR spectroscopy.

3. In another application the Pneumatically Focused gaseous fraction ofthe sample may be subjected to either uv, visible, IR or otherwavelength absorption measurements in a waveguide, such as a metallic ormetallic coated waveguide. In such applications the approximately linearincrease in refractive index of the gaseous sample with pressurizationcould enable the total internal reflection of the propagated beam.

U.S. Pat. No. 5,892,861: “Coated optical waveguides as extremely longpath sample cells” (April 1999) states that:

-   -   A very long sample cell for spectrophotometric measurements that        can be used to extend sensitivity to very low levels of gaseous        components, under about 50 parts per billion. The cell is an        optical fiber positioned within the annular space of a housing,        with a gas stream flowing along the annular space. The outer        surface of the fiber is coated with a material, e.g., an        adsorbent that concentrates at least one component of the gas        stream at the interface of the fiber and annular space. An        indispensable prerequisite is that the coating have a refractive        index greater than that of the optical fiber core. Radiation is        propagated along the core of the fiber, and the evanescent wave        passes through the adsorbed component, ultimately changing the        radiation detected at the output end of the fiber according to        the nature and concentration of the component. What we have done        is to construct an extremely long sample cell for        spectrophotometric measurements using an optical waveguide, or        optical fiber, as the underlying component.

This waveguide cell operates by adsorption or absorption of targetanalytes on the waveguide coating material. No provision is made foradjusting the flowing sample pressure in the waveguide absorption cell.In contrast, in the present disclosure the pressure could be adjusted toquite high levels by suitably strengthening the waveguide material or byproviding a strong external cladding. The increased pressure may providethe following additional advantages over those claimed by U.S. Pat. No.5,892,861.

-   -   1. Increased pressure may enhance adsorption of trace analytes        in the sample stream.    -   2. Increasing pressure prior to entering the waveguide cell may        remove condensable vapors within the sample (for instance,        water) which could interfere with the absorption measurement.    -   3. Increasing and decreasing pressure within the cell may        accelerate adsorption and desorption of the target analytes,        resulting in faster time response.    -   4. In addition to 1-3 and in contrast to U.S. Pat. No.        5,892,861, the absorption may alternately be carried out        homogeneously (without adsorption to a coating material) under        the following conditions.        -   a. the gas to be analyzed is pressurized such that its            refractive index reaches a much higher value. Such            refractive index is generally proportional to pressure.        -   b. The waveguide itself, or any appropriate coating thereon            has a refractive index greater than the compressed gas.            Although such waveguide material may not now exist it should            be developed.

Under these conditions the sample/waveguide will serve to transmit theanalytical probe beam over long distances due to total internalreflection, resulting in high sensitivity. Furthermore, said waveguidecan be coiled (with some loss in transmission), thereby producing anabsorption cell which is more compact.

Thus Pneumatic Focusing technology will complement and extend theusefulness and sensitivity of waveguide absorption measurements such asdisclosed by U.S. Pat. No. 5,892,861 and other such waveguide patents.

When air or other sample gases are compressed to higher pressures, anyreactions which may be occurring within the gas sample likely areaccelerated, since reaction rates are proportional to the product of thereactants' concentrations.

As an example, ozone reacts with alkenes in ambient air. If such air ispressurized, for instance by a factor of 10, these reactions will occurfaster, in this case by a factor of 100. However, the rate of fractionalalkene removal per unit time by the reactive ozone will be increasedonly by a factor of 10. Thus is it known within the field of atmosphericmeasurements to remove ozone from a gas sample before either storing itfor later analysis, or passing in into any sort of collection offocusing device. This standard technology may be applied to PneumaticFocusing as well. Standard methods of ozone removal include reactionwith added nitric oxide (NO) or removal on some surface, such as acopper surface, or a glass fiber surface which has been coated withreactive potassium iodide (KI). In a current disclosed embodiment acopper sample loop was employed.

Chemical reactions which remove analytes may present problems which mustbe addressed (for instance as described in the last paragraph). Suchreactions may also be used to advantage in Pneumatic Focusing. One suchexample is the measurement of atmospheric nitric oxide (NO). A currentpopular method for measuring NO is O₃ to draw a air stream sample intoan instrument while adding ozone O₃ from an ozone generator. Thisproduces a chemiluminescent reaction NO+O₃→NO₂*(in an excited electronicstate)→NO₂+light. The chemiluminescence emission, which may be detectedby a phototube, is proportional in intensity to the product of the NOand O₃ concentrations. Since in many atmospheres both NO and O₃ arepresent together, Pneumatic Focusing (which accelerates the rate of thisreaction proportional to the square of the pressurization ratio) willgenerate an emission whose time-varying intensity is proportional to theproduct [O₃][NO]/[P]. The term [P] in the denominator of this expressionrefers to quenching of the emitting state NO₂*. Thus the fluorescencesignal should increase proportional to pressure. Further, the integratedintensity is proportional to the concentration of whichever of these twomolecular species is in lesser concentration (the limiting reagent).These two pieces of information will allow the individual concentrationsof each to be inferred. This method is superior to existingchemiluminescence because it is simpler and provides information aboutboth species' concentrations. Of course, its effectiveness depends uponboth species being present. If only one is present (such as at nightwhen the species present in excess may titrate away the other), then theabsent species may be added. Unlike traditional chemiluminescencehowever, it need not be added in precisely regulated concentration.

For FID measurements, a fuel gas must be provided. Working systems usedhydrogen (H₂) gas from compressed gas cylinders as fuel for the FID.There are other methods for providing the fuel gas for FIDs. Forexample, other embodiments could use any of several, commerciallyavailable electrolytic hydrogen generators. One example of such acommercially available generator is Restek Model No. 75-32, which issold commercially by Restek, of Bellefonte, Pa. These electrolytichydrogen generators are especially suitable for conditions whereexplosive hazard is a concern.

For FID detectors, air or oxygen may serve as a source of an oxidizerfor the FID flame. Moreover, air or oxygen powers the pneumaticallydriven sampling valve 16 in FIG. 1. A working system used compressedcylinder air or oxygen. Other applications might use ambient air as asource of an oxidizer, which ambient air would be delivered to the FIDby a compressor. Suitable compressors are commercially available, suchas Model No. Jun-Air 200-1.5 BD2, from Restak, of Bellefonte, Pa. Suchcompressors also could produce compressed air as the carrier gas.

6. Pressure Regulators

Pressure regulators are used to deliver controlled flows of compressedgases, some of which are discussed above, at a substantially constantoutput pressure from the cylinders or compressors to the chromatographicinstrument. Typically regulators are capable of delivering pressuresabove ambient from about 1 psi to about 4,000 psi above ambientpressure. Pressure regulators set to a predetermined, but substantiallyconstant pressure, have been used in working embodiments. These pressureregulators also might be controlled by a computer. Computer-controlledpressure regulators would allow for pressure programming of eitherPneumatic Focusing, chromatographic separation, or both. Special highpressure regulators can be used for the carrier gas or PF gas inPneumatic Focusing.

7. Reagent Gas Clean-up Traps

Contaminant traps, particularly carrier gas traps, have been used incombination with working embodiments of the present apparatus. Suchsample traps typically consisted of galvanized pipe and appropriatefittings for coupling to the carrier conduits used with the apparatus.The sample traps used with working embodiments typically are filled withmaterials, either alone or in combination, to remove impurities from thecarrier gas (often helium), O₂ or H₂ for the FID. Examples of materialsto be used include mixtures of molecular sieves, activated charcoal, andmixtures thereof. Other materials that remove impurities from thecompressed gases sufficiently to allow the use of low-purity gases andthereby lower the operational costs of the instrument, also can be used.

Contaminant traps used with working embodiments were prepared by fillingthe trap with appropriate packing material, glass wool caps and frits,which prevent the packing material from being transported into thesample loop or chromatographic column. In one working embodiment castiron pipe fittings were used to form a contaminant trap which was filledwith activated charcoal for carrier gas cleanup. Working traps werebaked in an oven with low helium, or other purge gas flow, at atemperature of, for example, about 100° C. Other temperatures can beused, if desired, to remove any adsorbed impurities before the firstuse, or after excessive amounts of impurities have built up by using thesample traps. Suitable traps can be made. Suitable sample traps also arecommercially available, such as Restek Gas Management System or purifiertube, catalog No. 21660, available from Restek, of Bellefonte, Pa.Alternatively, high-purity compressed gas cylinders could be used.

8. Tubing for Transporting Compressed Gases

Tubing is needed to transport compressed gases from the compressed gassource to the chromatographic instrument. Working embodiments of thepresent apparatus used ⅛ inch outer diameter metal tubing such as coppertubing, to transport compressed gases to the chromatographic instrument.Small diameter tubing is less expensive and is better able to withstandthe high-pressure focusing gas associated with pneumatically focusinganalytes in a sample. Tubing made from materials other than copper couldbe used as well. For example, tubing made from other metals, plastics,or combinations thereof, also can be used. The selection of anappropriate material for making such tubing will depend, in large part,on the particular application. Using high pressure in enclosed volumescarries a significant explosion safety issue. In any PFGC applicationsappropriate safety precautions must be employed.

9. Fittings for Connecting Components of the Apparatus

Standard taper pipe fittings and Swagelok brand fittings have been usedwith working embodiments of the present apparatus to connect variouscomponents of the regulators, traps, and tubing to the chromatographicapparatus. Persons of ordinary skill in the art will realize that othertypes or brands of fittings may work equally well and also may becheaper or more suitable for a particular application.

10. Chromatograph

A schematic of a typical chromatograph is provided by FIG. 7, fromBoyer's “Modern Experimental Biochemistry,” Benjamin/Cummings PublishingCo. (1993). Two working embodiments of the present apparatus usedin-house-modified Varian model 3400 and 3700 gas chromatographs with afactory-equipped flame ionization detectors. The Varian 3700 instrumentwas modified as follows for either gaseous or liquid samples.

1. Liquid phase injection PFGC. Refer to FIG. 8. The standard syringeinjection port 150 was modified for automated liquid injection asfollows. The syringe injection/septum containing cap (not illustrated)was unscrewed and not used. The injection assembly was removed and theseptum purge tubing was cut off. A brass tube 152 was machined to 0.259″od and {fraction (1/16)}″ id and placed into this injector body 154,which transferred heat from the heated injection manifold to the{fraction (1/16)}″ tubing leading from the sample injection valve 156(Valco 8-port valve). Upon sample injection from the sample loop (notshown) to the chromatographic column 158 the liquid sample passedthrough the heated injection block and associated fittings andvaporized. A standard Swagelok ⅛″ to {fraction (1/16)}″ reducing union(#B-400-6-2) 160 was modified to additionally perform a check valvefunction by boring out the interior to accept a ⅛″ stainless steelbeebee 162. A plug was inserted from the large end to contain the beebeeand the fitting was cross-drilled to accept an epoxied in pin 164 tocontain the beebee. This check valve prevented backflow of columncarrier gas into the downstream end of the sample loop upon sampleinjection. Sample from injection port 150 was coupled to column 158 by aSwagelok reducing union 168. FID 170 was operably coupled to the column158. The vaporized liquid sample, i.e. a gas, was pneumatically focusedby the high column pressure so that column flooding did not occur. Heattransfer/vaporization could be controlled by a combination of injectionblock 150 temperature, injector insert 152, tubing 166 id, and carrierflow rate. If desired, additional bypass plumbing could send only aportion of the carrier gas through injector 150.

2. Gas phase injection PFGC. The integral carrier gas flow controlvalves and syringe injection ports were disconnected from the carrierflow and need not be used to provide the gas-injection PneumaticFocusing apparatus. These components would not be required if the gassampling instrument were built initially, instead of being made bymodifying existing chromatographs. Avoiding using carrier gas flowcontrol valves and syringe injector ports would make the presentinstrument more compact and less expensive than currently availablechromatographs that can be modified as described herein. Instead, thecarrier gas is brought directly to one port of a multiple-port samplingvalve. One working embodiment of the present apparatus used an 8-portsample valve, namely Valco Model A28UWP 8 port, ⅛″, 2-position valve.Other commercially available multiport valves could be used, dependingupon the application. For instance, in another working embodiment ofthis device, a similar 10 port valve was used, which allowed two samplesin two sample loops to be simultaneously injected into two columnsrunning into two separate detectors in a single gas chromatograph. Thiswould allow compounds of varying chemical nature to be subjected todifferent levels of separation.

In some instances it would be more suitable, and perhaps less expensive,to use individual valves to perform these functions rather than a singlemultiport valve. For example, using plural individual valves instead ofa single, multiport valve could allow greater and more precise controlof the pneumatic sample focusing. An embodiment of this 3 three-wayvalve setup has been constructed using B41XS2 Swagelok valves capable ofregulating pressure up to 2,500 psi. Electronic motor actuatorsconstructed for that purpose controlled these valves. The carrier gascylinder regulator controls carrier gas flow pressure. Workingembodiments used a cylinder regulator. Cylinder regulators typicallyprovided a gas pressure of from about 300 psi to about 500 psi. Althoughregulators that provide gas pressures of from about 300 psi to about 500psi are described herein, other regulators that provide equal, andespecially higher pressures, would be as desirable, or likely even moredesirable. This would include pressures high enough to convert somecarrier gases to supercritical fluids. Regulators providing gaspressures greater than about 400 psi would allow using either largersample sizes, or greater Pneumatic Focusing (higher pressure) or both.This would provide better chromatographic resolution, highersensitivity, or both. Of course, as pressure within the column isincreased, a consequential decrease in resolution may occur due toslower diffusion rates, thereby producing an optimum pressure that maybe found by a combination of theory and/or experiment.

At such head pressures, the carrier gas flows through the sampling valvedirectly to the column with the valve in the sample position. Flow ratethrough the column in a working embodiment of the apparatus wascontrolled by a PNEUMADYNE (nickel plated brass) valve CS70303. ThePNEUMADYNE valve was placed on the downstream end of the chromatographiccolumn but before the FID detector. The PNEUMADYNE valve includessilicone o-rings to withstand the high chromatographic oven temperatures(e.g. 200C). Another approach for regulation of high pressure flowswould be as described by E J Guthrie and H E Schwartz in “Integralpressure restrictor for capillary SFC” Journal of ChromatographicScience 24 (1986) pp. 236-241.

In a working embodiment of the present apparatus the sample loop andcolumn pressure were maintained substantially constant at about 300-500psi through the chromatographic analysis. A more suitable andefficacious approach in some applications would be to drop the carriergas pressure to a pressure more typical of conventional gaschromatography used for standard VOC analysis, such as to pressures ofabout 30 psi to about 60 psi, and open the flow-regulating valve toallow constant or reduced mass flow of eluting carrier gas and analytesinto the detector, while maintaining the chromatographic column at lowerpressure during the analysis. There are several reasons for thispressure reduction, including (1) to limit the carrier gas flow rateexiting the separatory column for subsequent analysis by, for example, amass spectrometer, and (2) better resolution may be obtained at lowerpressures, or (3) lower carrier flow rates would use less carrier gasand be more economical. Maintaining the chromatographic column at alower pressure could provide greater separatory efficiency due to higherdiffusion rates of the analyte/carrier gas mixture during elution. Also,with some types of detectors, especially mass spectrometers (MS),effluent should be limited to 1-2 standard cubic centimeters/minute. Inthe current technology, after expansion past the flow/pressureregulating valve at the end of the column, carrier flow increases to anadjusted value of 20-40 cubic centimeters/minute. In other practicedifferent flow rates might be as suitable or more suitable. 40-60 cc/minwas suitable for the FID employed in one working system, but likelywould be unsuitable for an MS instrument. Splitting the flow out of thehigh-pressure capillary column might be disadvantageous for sensitivity,as less sample would enter the MS. Thus, dropping the carrier pressureand opening the valve under computer control after column injection isan important variation which would use the adsorptive property of thecolumn to enhance sensitivity by increasing the relative partialpressure or mole fraction of the analytes in the carrier gas. Anotherapplication would allow pressure programming of the carrier gas, whichwould be especially suitable if the carrier were a supercritical fluid.Still another would be to carry out gradient elution with two or morecarrier gases. Furthermore, after exiting the column, the flow couldequally as well be split between a number of detectors arranged in acombination of parallel and series, depending upon their method ofdetection, thereby giving multiple responses for individual or varyinganalytes.

a. Pneumadyne Valve

-   -   The PNEUMADYNE valve described above as received from the        factory was modified (FIGS. 9 and 10) for use with the present        system. More specifically, FIG. 9 shows a valve 200.        -   i. The inlet fitting 202, a {fraction (10/32)} tapered pipe            fitting, was rethreaded with a {fraction (10/32)} dye for a            straight {fraction (10/32)} thread, and machined to produce            a tapered inlet. These modifications were made to allow its            connection to the capillary column.        -   ii. The outlet fitting 206, a {fraction (10/32)}            straight-threaded cavity was fitted with a hollow, {fraction            (10/32)} stainless steel screw 208, permanently glued into            the valve body. This modification was made to allow its            connection to the short section of capillary column leading            to the FID. High T glue withstood 280° C.    -   b. The PNEUMADYNE valve was connected to the outlet of the        chromatographic column. This connection can be made in any        suitable manner. In a working embodiment, the PNEUMADYNE valve        200 was connected to the outlet of the chromatographic column by        inserting it through a SWAGELOK {fraction (1/16)}″ cap nut, then        through a suitable graphite ferrule 208 and then inserting it        into the rethreaded aperture to a point just above the tapered        valve needle. The SWAGELOK nut was tightened onto the rethreaded        valve inlet pipe, compressing the graphite ferrule into the        tapered inlet prepared for that purpose and around the capillary        column. This formed a hermetic seal, which was capable of        withstanding the high pressures, i.e., in a working embodiment        of from about 300 psi to about 1,500 psi, as required for        Pneumatic Focusing and delivery of the sample, particularly air        samples. In making this connection it is important not to        project the capillary column so far into the valve that it will        be contacted and crushed by the valve needle as the valve is        sealed off. Commercially available PNEUMADYNE valves generally        are not rated for the high pressures of the carrier gas system.        But such pressures occur within the valve only upstream of the        flow-controlling needle. The pressure of the carrier gas drops        past the needle to much lower values as such gas, or gasses,        pass through the valve body and enter the outlet capillary tube,        which carries any gas or gasses to the FID with little back        pressure.    -   c. This commercial Pneumadyne valve performed satisfactorily in        the working embodiment described herein but was difficult to        adjust to the correct pressure and should eventually be replaced        with a suitable high-pressure valve either purchased or designed        a priori. Another commercial valve, or valves designed for this        specific purpose, may work equally as well or better and be more        suitable. One such valve 250 has been designed based upon the        Pneumadyne valve described above. With reference to FIG. 10 in        this modification, the high temperature portion 252 of the valve        250 where the needle 254 regulates flow would be filled with        epoxy; the needle 254 would be coated lightly with grease to        prevent adhesion to the epoxy, and would be inserted into the        soft epoxy to form a channel. After the epoxy hardens, the valve        250 would be withdrawn and then scratched one or more times        longitudinally with a diamond pencil or other suitable device.        If epoxy filled the outlet channel during manufacture it could        be drilled out with a very small drill though port 255. These        scratches 256 would then form the flow regulating channels when        the needle was reinserted into its epoxy seat. Since the epoxy        will be somewhat softer than the needle material, exertion of        pressure on the needle 254 by firmly threading it into the seat        will result (if necessary for further regulation) of an        extrusion of the hardened epoxy slightly into the scratched        channels, further reducing flow rates to the low values required        in this high pressure application. The redesigned flow        regulating valves should work effectively, perhaps better than        those valves used in working embodiments described herein. It        should be understood that the above design is to modify an        existing gas valve as a cost savings measure during development.        In actual implementation it might be and probably would be more        efficacious to design and have machined a similar filled-body,        scratched-needle valve from scratch, following the design of        FIG. 11. In such a valve header or otherwise move suitable        materials (e.g., stainless steel) would be used rather than        nickle plated brass.    -   d. Commercially available PNEUMADYNE valves also have dead        volumes. Dead-volumes associated with chromatographic systems        generally are undesirable because they reduce resolution by        mixing or remixing separated sample components. Although the        PNEUMADYNE valve was not designed as a chromatographic valve and        does contain significant dead volume, this dead volume is of        minimal consequence with respect to the present apparatus, and        method for its use, for the following reasons. Pneumatic        Focusing is currently achieved in the sample loop and        chromatographic column by the helium carrier gas. Pneumatic        Focusing in one working embodiment of the apparatus has been        achieved at a pressure of from about 300 psi to about 500 psi.        Upon flowing past the needle, the carrier gas drops to a        pressure near atmospheric (ca. 15 psi). Thus the gas expands by        an approximate factor of 20-30, thereby sweeping out the valve        dead volume in a minimal amount of time without remixing        separated peaks.

The Pneumadyne valve incorporated in working embodiments of PFGCdescribed herein was barely adequate for desired performance. A moresuitable valve would allow greater flexibility of adjustment, includingcomputer-controlled adjustments. Shortcomings of the pneumadyne valveincluded (1) difficulty and irreproducibility of adjustment—the valvehad to be adjusted ‘off’ to obtain low enough flows and (2) temperaturestability. Although one valve successfully injected more than 10,000samples, other valves had a tendency to respond to oven temperatureprogramming by adjusting internal needle position so that flows jumpedfrom set values. Usually this stopped after a break-in period. If not,the valve was removed and reconnected or discarded for another valve.More suitable valves may be commercial available and have likewise beenherein designed and described.

It is possible that, in some applications, such as when the columnpressure is dropped to lower values and the valve opened after injectionof the sample on the column, the dead volume in the current PNEUMADYNEvalve may not work as effectively due to lower volume flows. In suchcases, more suitable commercial valves could be employed, for instanceliquid or SCF chromatograph valves. One such design has been describedabove, wherein the filled valve interior will significantly reduce deadvolume while enabling more precise and reproducible flow regulation.Such a valve could more profitably be designed and built from scratchusing more suitable materials without epoxy.

For instance the Pneumadyne valve could be replaced with a low deadvolume shut off valve. The valve would be closed during PneumaticFocusing/injection. Subsequent to focusing/injection the valve wouldslowly open, as the column head pressure is automatically dropped to30-60 psi. This would allow bleeding of the high column pressure slowlythrough the column and into the FID. Subsequent elution would occurunder “normal” chromatographic conditions. This application would besuitable for Mass Spectrometric detection.

A pressure gauge (not shown) can be coupled to the valve 30 in FIG. 1.This pressure gauge can be used to adjust the pressure of and/or linearflow rate through the system. The pressure gauge can be placed undercomputer control to continuously and automatically adjust the pressureand/or linear flow rate through the system. Computer controlled flowregulation is advantageous in pneumatically focused gas chromatographyto be able to independently vary flow rate and pressure under computercontrol. Pressure may be regulated with a computer controlled pressureregulator. In this application, flow would be regulated by computercontrol of the downstream valve. A Pneumadyne Valve CS70303 was modifiedas described herein.

This valve also has been modified to include an aperture in thesidewall. With reference to FIG. 11, a valve 220 was tapped for 10-32threads and fitted to a second hollow 10-32 screw 221 by gluing withhigh temperature epoxy. See FIG. 11. The outer end 222 of this screw wasmachined with an internal taper top to accept a graphite ferrule 223.The cap nut was a {fraction (1/16)}″ Swagelok cap nut as describedpreviously. This extra port could be connected by a length of shout,open capillary column to a small volume pressure gauge from which thecomputer could read the pressure. This pressure-to-flow transducershould be calibrated by disconnecting the capillary column from thedetector and extending it slightly outside the gas chromatograph and toa flow meter. Flow rate then should be varied with computer control ofthe modified valve and measured with the flow meter. Concurrently, thecomputer records the resultant pressure value for each measured flowrate as controlled by the valve setting. This procedure establishes acalibration curve which may be repeated for different oven temperaturesand column head pressures. In this fashion, the computer can establishthe desired flow rate for any head pressure or column temperature byempirically varying the valve position until the desired pressurereading according to the calibration table is obtained. This valvecontrol may be carried out as desired before or during a chromatogram.

Conventional systems which do not use Pneumatic Focusing commonly use“makeup gas” when operating at more usual pressures of from about 30 psito about 60 psi. “Make up” gas is used in conventional systems to sweepthe column outflow more rapidly into the FID detector. No makeup gas isrequired with the apparatus and method presently described, a furtherdesign simplification.

-   -   e. The PNEUMADYNE valve was connected to the FID. In a working        embodiment, the PNEUMADYNE valve was connected to the FID by 20        centimeters of capillary tubing. A person of ordinary skill in        the art will appreciate that this connection can be made using        any suitable method and material. In a working embodiment, a        short (ca 20 cm) section of the same column material that was        used in the separatory portion was used to connect the        PNEUMADYNE valve to the FID. The valve outlet connection was        made in the same manner as the valve inlet connection. This        column material used to connect the PNEUMADYNE valve to the FID        was placed just below the actual flame of the FID. The position        of this column material was established empirically to:        -   i. not burn the column end in the flame;        -   ii. not extinguish the flame; and        -   iii. give maximum signal subject to i and ii.

It will be appreciated that other types of tubing could be used toconvey the column effluents to the FID or to a manifold, which woulddirect some fraction of the effluent to any of a number of parallel orserial detectors. Or, the valve could be connected directly to thebottom of the FID housing by suitable connectors thus eliminating thecapillary conduit.

Moreover, persons of ordinary skill in the art will appreciate that anyof numerous other commercial gas chromatographs [or high pressure or SFCor liquid chromatographs] with a variety of different detectors could bemodified as described herein. It also would be possible to construct amore compact, more portable, safer, cheaper, or otherwise more favorablydevice than the working embodiments of the present apparatus describedherein and made by modification of commercial instruments.

11. FIDs Having Fuel and Oxidizer Flow

A FID is operated with fuel flows, such as flows of hydrogen, and anoxidizer, such as air or oxygen. The flow of fuel and oxidizer areempirically optimized to provide maximum response while allowingcontinuous flame operation. Oxygen is a more expensive oxidizer thancompressed air. However, oxygen provides several advantages. Forexample, oxygen requires lower volume flows and thus less frequentcylinder changes. Oxygen also provides an apparent higher response tothe eluting VOC compounds. It has been confirmed that oxygen supplied tothe FID in place of the more commonly employed air produces a higherresponse to at least some hydrocarbons. Substitution of oxygen for airin the FID produces a significantly higher response for some atmosphericVOC hydrocarbons. Since Pneumatic Focusing often will be employed in themeasurement of trace gases at very low concentrations, using oxygenwould be very advantageous. An additional advantage is that oxygencylinders will last significantly longer than compressed air cylindersbecause nitrogen is not required for combustion, but is rather adiluent.

Alternatively, compressed ambient air delivered to the FID may obviatethe need to use an air cylinder and regulator. This further simplifiesthe instrument and may make it less expensive to operate remotely. Thiscompressor could also supply compressed ambient air as the carrier gas.Flows of fuel and oxidizer are passed through the chromatograph'sstandard inlet valves and conduits. The flow rates of the fuel andoxidizer are regulated by a combination of empirically determinedcylinder regulator pressure and chromatographic settings. Currently,suitable operating pressures for fuels and oxidizers are as follows: (a)if hydrogen is used as a fuel, then the operating hydrogen pressure isfrom about 30 psi to about 60 psi, with about 50 psi being a currentlypreferred pressure; (b) if air is used as an oxidizer, then theoperating air pressure is from about 60 psi to about 100 psi, with about80 psi currently being preferred; and (c) if oxygen is used as theoxidizer, then the operating oxygen pressure preferably is from about 15psi to about 30 psi, with about 20 psi being a currently preferredoperating pressure for an oxygen oxidizer flow. Such pressures are afunction of the original instrument flow control valve settings.

12. Signal Processing, Amplification and A/D Conversion

Working embodiments of the present apparatus used a FID, although otherdetectors also could be used. For instruments using FIDs, currentpassing though the FID electrodes is received by a factory-installedcoulometer and then passed as a voltage to ports on the side of theinstrument. The signal is conducted by coaxial cable into an amplifier,such as a 1000× amplifier. The amplified signal may be filtered, ifdesired, by an onboard filter.

The amplified signal is then passed to an analog-to-digital converter.Any suitable A/D converter can be used. A working embodiment of thepresent apparatus used a COMPUTER BOARDS analog-to-digital converter,Model No. CIO-DAS08Jr/16-AO. A working embodiment of the currentapparatus used a modified 16 bit CIO-DAS08Jr/16-AO A/D converter. Themodified 16 bit CIO-DAS08Jr/16-AO A/D converter was modified for anextended range to accommodate either very large peaks or upward drift ofthe chromatographic baseline associated with temperature programming.This modification consisted of a computer-controlled analog offset tothe to the A/D board, which allowed successive voltages greater than thenormal range for the A/D board to be accepted. This automatic offset wasdone by computer control. Using this novel offset procedure, the rangeof the 16 bit A/D board has been significantly extended beyond the usual65,000 range, such as to 700,000, i.e., an effective 19 bit board. FIG.12 is a control circuit for the A/D board, and FIG. 13 is an amplifiercircuit to increase voltage of signals for the A/D board.

Another application of this analog offset to a gas chromatograph wascarried out by a novel subroutine in the signal acquisition programgc.bas which is described next. This program determines the baseline ina given computer-acquired chromatogram by selecting signal points whereno peaks are eluting. A group of these data points are then fitted witha polynomial of desired order, for instance 5th to 15th. This curve fitthen becomes the baseline for the next computer acquired chromatogram.Before each point is acquired from the AID board, it is offset by thecomputer fit baseline value of the previous point. In this way acompletely baseline-corrected chromatogram appears on the screen and isstored for later viewing and analysis. The program gc.bas also storesthe polynomial coefficients so that the original data may easily beregenerated if desired.

Gradual drift of the baseline is handled in the program by subtractingthe polynomial-fitted baseline of the 2nd to last chromatogram from thepolynomial-fitted baseline of the last chromatogram so that an absolutereference baseline is maintained.

13. Computer Sampling Control for Baseline Determination and InternalStandard Addition

A C Lewis N Carslaw et al. In “A larger pool of ozone-forming carboncompounds in urban atmospheres, Nature 405 (2000) pp. 778-781 havepointed out that the current state of the art in measuring atmosphericVOCs misses a significant fraction of VOCs which are unresolved and forman increased baseline under the resolved peaks. These authors determinedthe ‘missed’ unresolved compounds by subjecting an ambient air sample tothe powerful new technique of 2-dimensional chromatography. If true,this paper has discovered a significant source of error in VOCmeasurements and potentially pollution and emission control. Thissituation has been subsequently discussed by AC Lewis in “NewDirections: Novel separation techniques in VOC analysis pose newchallenges to atmospheric chemistry” in Atmospheric Environment 34(2000) pp. 1155-56.

Two types of error should be distinguished.

1. Some compounds because of high molecular weight or high polarity orfor other reasons may not elute on a given chromatogram. These compoundsremain on the column for extended periods of time, eventually incontinuous operation forming a temperature dependent ‘baseline’ increase(bleed) during temperature programming. These may be termed residualcompounds.

2. Other compounds are eluted in the chromatogram in which they wereinjected, but because of individual low concentration and large numbersare not individually resolved and hence show themselves as an increasedbaseline (bleed) which is not immediately distinguishable for othercauses of baseline shift with temperature programming.

Fully automated Pneumatic Focusing gas chromatography is completelycompatible with 2-dimensional analysis of focused ambient air or othergaseous samples. However, another, simpler approach is also possible. Inautomated Pneumatic Focusing gas chromatography, since the gaschromatograph is under complete computer control it is possible toinject standards or determine the baseline whenever desired. Thus thecomputer can perform a true baseline measurement by any of severalmethods. This baseline measurement also serves to detect the presence ofany spurious or artifact peaks, such as might be present in the carriergas. In this approach the ‘true’ baseline to a chromatogram isdetermined by injection (under computer control) of a sample which hasno significant VOC concentration.

Another application is the injection of calibration standardsalternately with actual sample analysis. Such injections can be carriedout automatically under computer control, for instance one a day, once aweek, or every other sample as the situation warrants. Both baselinedetermination and standard addition involve similar concepts andprocedures. Some of these baseline determinations involve admission ofgases from reference cylinders to the Pneumatic Focusing system. This iscarried out by the control computer through the parallel port usingcircuitry shown in FIG. 14.

FIG. 14 shows a calibration injection device 1400. Device 1400 includes25 pin cable 1402, coupled to solenoid control unit 1404, which ispowered by a power cable 1406. This device 1404 controls three-way valve1408 through control cable 1410. Three-way valve 1408 divertscalibration gas inlet 1412 or sample gas inlet 1414 to gas chromatograph1416.

For either case, any of the following methods may be used.

1. A zero air sample (commercially available) is contained in apressurized cylinder and periodically injected under computer controlinstead of a true sample. This sample should show no peaks and representthe true instrumental baseline, incorporating the column baseline bleedas well as baseline 1 above.

2. As in ‘1’ except that any desired standard compounds are added to thezero gas sample. Such compounds are chosen for appropriate retentiontimes and will not interfere with the determination of the ‘true’baseline as they will form well behind peaks.

3. The actual sample is passed through a VOC filter containing, forinstance, activated carbon such has been described in carrier gascleanup. This filter may not remove methane quantitatively whichpresents no problem.

4. As in ‘3’ except any desired standard compounds are added to thepurified air sample via permeation tubes or other suitable methods.

5. As in ‘3’ or ‘4’ except that a matched, dual column gas chromatographis employed with VOCs removed by filtration from one column with anunfiltered air sample going to the other column. These two flows areswitched on each injection so that any possible variation betweenresponse is seen and so that residual (very slowly eluting compounds)are equally distributed between the two columns.

6. Following analysis of an actual air or other sample the sample valveis NOT returned to the sample mode. Thus pressurized carrier gas(helium) remains in the sample loop and is injected during the nextsample processing cycle.

7. As in ‘6’ except that any desired internal standards are added to thehelium carrier gas. Such standards need not interfere with the ‘true’baseline determination and should be chosen not to elute with targetanalytes.

8. The sample valve may not be thrown at all, rather the GC goes througha temperature programming cycle with no sample injection at all.

9. As in ‘8’ standards are added to the helium carrier, collect at thecolumn head during cool down of the oven, and form standard peaks upontemperature programming of the oven.

In any of these cases, if the air zero or helium carrier is pure (whichis the case with proper filter implementation) then any of thesebaseline chromatograms can represent the baseline for previous andsubsequent chromatograms. Two types of ‘unresolved/undetected’ compoundsare distinguished above. So long as the baseline determination is notperformed too frequently, it should distinguish only the second typeabove, as the high molecular weight compounds from previous injectionswill still contribute to the baseline during the application ofprocedures a-h above. Such compounds should be in quasi steady stateafter several injections, and should not change significantly in theircontribution upon the intermittent injection of any of the above ‘clean’samples.

If these are significant compounds in case 1 above to be measured, amore appropriate column should be employed so that higher molecularweight, greater polarity, etc. compounds elute during an individualchromatogram.

Each of these approaches has its particular advantages anddisadvantages. Currently we prefer procedure ‘6’ for its ease ofimplementation (not requiring an additional gas cylinder) or the setupof FIG. 14 and its positive results. With ambient air sampling ‘7’ isnot required as ambient methane forms a satisfactory internal standard.FIG. 15 shows the determination of the baseline 1502 for an ambient airsample 1504. Subtraction of the ‘baseline’ chromatogram from the samplechromatogram shows (by difference, illustrated graphically in (FIG. 15)that these unresolved compounds make up about 10-30% of the totalresolved compounds total concentration. One advantage of procedures ‘1’or ‘3’ above is that either the ultrapure air sample or the heliumcarrier gas itself may contain one or more internal standard VOCs whichwill serve to calibrate the instrument in addition to determining thebaseline. For many air pollution applications it is not essential toknow the individual identities of the large number of unresolvedcompounds which 2-dimensional chromatography can resolve. In fact,simply identifying them would be quite an undertaking. Rather, by theirapproximate retention time these structures and molecular weights can beaccurately ‘assessed’ and their sum total concentration can bedetermined by the baseline subtraction procedure just described. Ineither situation, Pneumatic Focusing gas chromatography is the onlyfully-automated method to obtain information about both resolved andunresolved compounds in a gaseous sample.

14. Continuous Pneumatic Focusing

Most of the working instruments made to date have used what may betermed as ‘pulsed’ Pneumatic Focusing using pressure from a compressedgas cylinder. Single-stroke piston compression has been described aswell. A further type of Pneumatic Focusing, offering advantages in somecircumstances, is continuous compression Pneumatic Focusing. Acompressor has been used to deliver a continuous pressurized sample to aspectrometric cell. For a given compression/gas delivery capability, thesample pressure may be controlled by an outlet valve on thespectrometric cell. As the valve is closed, pressure rises in the cell.In this application, the focused sample has a residence time in the cellwhich may be calculated as follows. The STP flow rate of the gas may beexpressed as std cc/min as F, the cell volume as V and the compressionratio as R. The residence time tau in the cell (equivalent to the sampleaveraging time for analysis) is given by Tau=V/(FR). As in anycompression, provision for condensed water removal should be made. Inthis case, since the condensed water may contain analytes whoseconcentration is to be measured, it may be allowed continuously orperiodically (under computer control) to drop through a 2nd valve (FIG.6) into another spectrometric cell or be delivered to an additional gasor liquid chromatograph, pH or other ionic measurement cell, or any of amultitude of other analytical devices.

In other applications, such as spectroscopy, signal from the detectormay be acquired by other types of signal-processing devices. Examples ofsuch additional signal processing devices include, without limitation,coulometers, electrometers, counters, photo-multipliers, etc. Suchsignals can be subjected to any of several reported digital signalprocessing procedures, such as described by Lyons in “UnderstandingDigital Signal Processing,” (1997), incorporated by reference herein, toincrease sensitivity and reduce noise.

Any of a multitude of other A/D boards of the same or differentmanufacturer may be employed in signal acquisition. For instance, aCOMPUTER BOARDS 12 bit A/D board has been used in working embodiments ofthe present apparatus. The COMPUTER BOARDS 12 bit A/D board is capableof much more frequent readings, taking and averaging 100 points whereasthe 16-bit board only takes and averages 2.

Novel modifications of an analog-to-digital (A/D) board have been madefor acquisition and digitization of chromatographic or other analogdata, as follows.

A. In temperature programmed gas chromatography it is common for thedetector baseline to increase with temperature due to the increasingelution of compounds strongly adsorbed on the column as the temperaturerises. This produces a situation where the baseline itself may approachthe maximum signal an A/D board may obtain, typically −5 to 5 volts or0-10 volts. It is desired to have under computer control an offsetvoltage to extend the range of the A/D board to accommodate baselinedrift. Furthermore, it is common to wish to quantify a wide range ofpeak intensities. Under situations where large peaks and small peaks arepresent together, sufficient resolution to adequately capture smallpeaks may cause large peaks to go off scale on the A/D converter. Inthis instrument, a circuit (FIG. 12) was designed to offset the range ofthe −5 to 5 volt A/D board by incremental amounts of 5 volts to producea total offset range of approximately −50 to 50 volts. Operation of thisdevice is shown in FIG. 16. This illustrates the AID offset applied bythe computer program gc.bas whenever it senses that the signal is goingoff scale of the 16-bit range. The offset was programmed for this figureto show each application as a spike. There is no particular significanceto the data itself, other than it shows the high and low ends of therange which saturate the offset. The normal range of a 16 bit A/D boardis approximately 2^16 or 65,000. The observed range in this figure isfrom −32,000 to 40,000 for a total range of 72,000. This is equivalentto approximately 19.5 bits or an extension of a factor of 11 over thenormal range.

B. It is further desired to provide for interpolation between digitalreadings on an A/D board of any nominal resolution. For instance aComputer Boards Das08/Jr-AO 12 bit A/D board nominally can record 4095digital numbers. However, within the program gc.bas, provision is madefor taking and averaging 100 readings before recording the numericalvalue to computer memory and plotting on the computer screen. Althoughsuch averaging is not purely linear, its linearity is sufficient for thepresent instrument. With this averaging procedure it has been possibleto record an entire gas chromatogram using only the 35 digital numbersbetween −3895 and −3860 (out of 4095 available on the A/D board) sinceaveraged values are usable to interpolate between the nominal integervalues returned by digital reading (see FIG. 17). To clarify, for a 10 vfull scale 12 bit A/D board such as the Das08/Jr-AO, the minimumsensitivity is {fraction (10/4095)} or 2.4 mv. However, using theaveraging procedure within gc.bas and choosing an average of 100, it waspossible to increase the minimum sensitivity to between {fraction(1/10)} and {fraction (1/20)} of the nominal 2.4 mv, that is to 0.24 mvor even 0.12 mv, depending upon the rate of change of the voltage beingread. This is accomplished in the program gc.bas (enclosed) within thesubroutine ‘das8’ that acquires data from the A/D board. In operationwith the slower 16-bit A/D board only an average of 2 readings was taken(line 1105). However, with the 12 bit board discussed here, it waspossible to take 100 readings per save (ii=100 in line 1105) and stillfaithfully record the chromatogram. Typical peak data taken with thisaveraging procedure is shown in FIG. 17 and an enlargement thereof inFIG. 18. In FIG. 17 are displayed two chromatograms taken with anaverage of 100 readings per saved data point. The fastest rising peaks(e.g. at 13,000) have sufficient data for accurate representation oftheir areas. These peaks would have benefited from a reduction in theaveraging times perhaps. However, for the slowly rising peak around8,000, which is expanded in FIG. 18, between 10 and 20 readings aretaken per nominal integer A/D reading. There is an inherent and fairlyreproducible nonlinearly in these data which could easily be linearizedin software within the program or in postprocessing, giving betterlinearity.

15. Chromatographic System Control

The entire chromatographic system in a working embodiment was controlledby two computer programs. Most chromatographic functions of the Varian3400 are entered through a keypad on the front of the gas chromatograph(GC). Other commercially available GCs employ other types of control,including dials on the instrument front. Virtually all of theseinstruments can be adapted to provide the present apparatus, and can beused to practice the present method. Or, such a chromatograph could bedesigned and constructed from scratch.

Other functions of Pneumatic Focusing, including timing of valveoperation, are controlled by a personal computer. A working system useda 486 personal computer running WINDOWS 98. The computer program alsoacquired data from the A/D board.

A working embodiment of the present apparatus used a computer program,gc.bas, to further control apparatus functions. GC.bas was programmed inthe basic language TekBasic, running in a DOS window. However, suitableoperating programs may be written in other languages, such as TrueBasic, Visual Basic, GWbasic, other basics, Fortran, C, C+, C++, etc.GC.bas first sends a start signal to the chromatograph and then movesthe valve from a “sample air” mode to an “inject sample” mode.

The following keypad program was run on the Varian 3400 GC used to makea working embodiment of the present apparatus. Such programs can bealtered, if desired, for optimization for use with particularapplications. A program used with a working embodiment is described.Through the keypad, the following functions were entered to perform acontinuous sampling of the atmosphere using a working embodiment of thepresent apparatus.

-   -   1. initial range setting—10-10 amperes (low amplification for        methane measurement);    -   2. initial GC oven start temperature—35° C.;    -   3. auto zero output signal;    -   4. initial oven temperature hold time—3 minutes;    -   5. amplifier range—change to 10-12 amperes;    -   6. auto zero output signal;    -   7. initial temperature ramp speed—20°/minute;    -   8. intermediate column temperature—100° C.;    -   9. intermediate column temperature hold time—zero minutes;    -   10. secondary temperature ramp speed—5° C./minute;    -   11. final column temperature—200° C. (maximum recommended by        manufacturer);    -   12. final hold time—20 minutes;    -   13. reset oven to initial conditions, wait for start signal from        PC;

Additional chromatographic functions were performed by the personalcomputer, e.g., a 486 computer, running the laboratory-written Tekbasicprogram gc.bas (see the appendix) through the das16 a/d board. Certainof these functions are as follows:

-   -   1. A file is created on the computer's hard drive and named with        the month, day, hour and minute a particular sample is injected.        ASCII files are automatically created and named to hold the        individual sample data (i.e., the chromatogram), along with the        date and time a sample is injected. For example, a sample        injected on December 25 at 5:30 am would have a file named as        12250530.asc. Such files may be ‘zipped’ or otherwise compressed        to require less storage space.    -   2. A sample inject signal is sent to the sampling valve.    -   3. A GC start signal is sent to the GC.    -   4. A signal is acquired from A/D board, with a pause command of        30 ms. The pause allows a stable A/D board reading to be        obtained. Plural readings may be taken and averaged for storing        in the computer memory. In a working embodiment, two readings        were taken, averaged and saved. The average value is converted        to an integer to save storage space. 9.09 values are stored per        second, each an average of 2 readings. “Readings per second” are        controlled by software and may by reprogrammed to suit the        application.    -   5. A sample signal is sent to the sample valve. This returns        sample flow through the sample loop and carrier flow directly        through the sample valve to the chromatographic column. The time        this signal is sent to the sample valve can be an important        consideration. For example, upon “inject signal” to the VALCO        sampling valve from the computer, the following functions occur:        -   a. Carrier gas is diverted from a direct path through the            sample valve to the column and required to pass through the            sample loop before entering the column. The air sample is            diverted in the valve so it no longer passes through the            sample loop, but rather directly through the valve to the            sample pump.        -   b. Carrier gas, such as helium carrier gas, enters the            sample loop, which contains a sample, such as ambient air at            ambient pressure for analysis. The carrier gas drives the            sample before it to the end of the sample loop, through the            sample valve and onto the head of the separatory column.        -   c. The sample is compressed, and upon compression, the            sample both heats and loses ambient water vapor through            condensation. The extent to which the sample is heated is            controlled by the compression rate, thermal conductivity of            the apparatus and the temperature at which the apparatus is            maintained. Ambient water vapor condensation can occur            either to a fog, to the sides of the conduit, or a            combination of both. If desired, the end of sample loop            could be packed with material, such as glass beads, to            collect condensed water vapor.

U.S. Pat. No. 5,498,279 states that:

-   -   “High speed gas chromatography system for analysis of polar        organic compounds” describes Gas chromatography systems which        provide for high speed separation of polar compounds of interest        from samples which also include non-polar compounds. Efficient        separation is achieved through the use of a tandem series        connected combination of analytical columns, one of which having        a polar stationary phase material and another having a non-polar        stationary phase material. In two systems the order of the        analytical columns is reversed. Fluid flow conduits, valves and        vents are provided in a manner which eliminates mechanical        valves in a sample stream.”

Such patented process would work more effectively if coupled to analyzeeither the total condensed moist air sample or the water fractionthereof.

-   -   a. The timing of the valve return to the sampling position is        determined experimentally. For ambient air samples, the valve        return timing generally is set to a point at which the (probably        unretained) methane has all entered the column. This is        determined by experiments in which the valve timing is changed,        chromatograms are obtained and the end of the methane peak on        such chromatograms is examined to see whether the methane peak        has been truncated. The sampling valve is returned to the sample        position at the earliest possible time. In a working embodiment,        the sample valve was returned to the sample position after the        799th readings of the FID, about 80 seconds. Returning the        sampling valve to the sample position at the earliest possible        time helps prevent condensed water from entering the        chromatographic column, and instead conducts it to the waste        stream entering the sampling pump. Returning the sampling valve        to the sample position at the earliest possible time helps (1)        eliminate much of the water in the initial sample from the        column; (2) deliver a constant amount of water to the column,        independent of the ambient humidity; and (3) quantiation depends        simply upon the quantity of sample in the sample loop volume,        which thereby allows for consistent chromatographic separations        from injection-to-injection, day-to-day, etc.    -   b. A preset number of readings is acquired. While acquiring the        preset number of readings, some, or all, readings are        sequentially displayed in real time on the computer screen. Each        reading is saved in computer memory. After the readings are        recorded, the program waits a sufficient period to allow the GC        oven to cool to a predetermined temperature. In a working        embodiment, a 7-minute waiting period was initiated by the        computer to allow the Varian 3400 GC oven to cool to a        temperature of about 35° C. The sampling cycle is then repeated.        In a working embodiment of the present apparatus, 38,000 FID        readings are taken over a sampling period of approximately 37        minutes, and the average of each pair stored in computer memory        for 19,000 stored readings. A person of ordinary skill in the        art will realize that the software can be changed to vary the        number and timing of readings, averaging of readings before        storage, and length of chromatogram.    -   c. The stored chromatograph can, such as through remote computer        access, be downloaded, such as through a network, to another        computer and processed as desired. Continuous computer data may        be acquired from the automated instrument operating anywhere        accessible by phone line, cellular phone, or satellite-linked        communication system. Continuously operating instruments may be        placed anywhere in the world with data acquisition occurring at        a central facility. The only normal human intervention required        to operate the system is to change the cylinder gases, if so        equipped, at regular intervals, such monthly. The computer can        be configured for automatic restart upon power interruption.        This processing includes a novel data analysis procedure, which        is described below.    -   d. Another application of this analog offset to a gas        chromatograph could be carried out by a novel subroutine (Sub        basetrack) in the signal acquisition program gc.bas which is        described below. This program determines the baseline in a given        computer-acquired chromatogram by selecting signal points where        no peaks are eluting. A group of these data points are then        fitted with a polynomial of desired order, for instance 5th to        15th. This curve fit then becomes the baseline for the next        computer acquired chromatogram. Before each point is acquired        from the A/D board, it is offset by the computer fit baseline        value of the previous point. In this way a completely baseline        corrected chromatogram appears on the screen and is stored for        later viewing and analysis. The program gc.bas also stores the        polynomial coefficients so that the original data may easily be        regenerated if desired.    -   e. The ambient air sample is drawn through a modified aquarium        pump FIGS. 3 and 4 to the Valco sampling valve and then to        outdoor air through ¼″ TEFLON tubing. This pump pulls about        0.2-1.0 liters/minute of outside air continuously through the        sample loop, except during the short time during each        measurement cycle when the sampled air in the sample loop is        pressurized and injected into the chromatographic column. In        this embodiment, any type of pump may be employed, since the        sample does not pass through the pump before entering the sample        loop/chromatographic column. In another application a pump was        modified (FIGS. 3 and 4) for suction rather than pressurization        by interchanging the internal check valves. FIG. 4 illustrates a        cross section of the pump 100. Housing holds diaphragm 114,        which is maintained in position by retainer 116. Retainer 116 is        coupled in position by pin 118.

With reference to FIG. 3, a pump 100 is illustrated for drawing airthrough the system. Pump 100 includes a housing 102 having an inlet 104.A tubing 106 houses spring 108, adjacent to which is positioned bb110.In other applications, the sample pump is replaced by any of severaltypes of compressors or pistons that serve to pneumatically focus thesample without the requisite of consumable high-pressure carrier gases.The sample loop in two embodiments consisted of 50′ of ¼″ of ⅛″ coppertubing connected to the Valco valve. As stated above, the sample loopmay be made of other metals, TEFLON or other plastics. The chosen sampleloop must withstand the Pneumatic Focusing pressures to be employed.Especially, the sample loop may be made of nickel tubing ornickel-plated copper tubing, since nickel has low adsorption efficiencyfor many VOCs or other gaseous sample analytes, or of copper to removeozone. The sample loop can be maintained at any desired constanttemperature by a thermostated heater thereby delivering a know volumeand mass of gas sample as governed by the ideal gas law PV=NRT or it'snonideal equivalents.

In one application the sample tube could consist of an optical orinfrared waveguide connected to a light absorption spectrometer so thatthe wavelength-dependent absorption of the Pneumatically Focused samplecould be determined after pressurization and before injection into thechromatograph. Such a cell also could be applied downstream of thecolumn to measure absorbance of the separated analyte components as theyelute from the column still at high pressure.

16. Piston Compression of Sample Gas for Pneumatic Focusing

In most embodiments to date compressed gases (often helium carrier gasin chromatography) have been used for Pneumatic Focusing. In thissituation care must be taken not to mix the focusing gas-with the sampleas described elsewhere. An alternate approach, which avoids the need forconsumable gas cylinders, is the employment of a compressionpiston/cylinder situation. One such prototype arrangement wasconstructed using a cylinder and a 12V electronic trailer jack (Atwoodcompany, purchased from a trailer supply distributor) to provide thecompression force. In one embodiment the jack was attached to anavailable cast iron table leg with stainless steel hose clamps. Thecylinder, which contained an o-ring-sealed piston, was similarlyattached. Application of 12V to the jack compressed the prototypepiston, which would drive the contained air sample into either aspectrometric sample cell or onto the head of a GC column.

The previous piston arrangement (available as surplus) is satisfactoryfor injections of small volumes into a chromatograph. However, in thecase of spectrometric Pneumatic Focusing it may be desirable to usecells of fairly large volumes (to minimize wall effects) and to use highfocusing pressures. In this case larger piston/cylinder arrangements arepreferred. The ability to compress at varying speed will be useful incontrolling compression heating of the gas as well as aerosolformation/growth via water condensation, which follows compression.

17. Computer Programs used for Data Interpretation

In addition to the program gc.bas, described above, which runs themeasurement cycle, acquires and stores the data, several other basiclanguage programs have been written for data interpretation. Forexample, the program, gc_mplot.bas plots a set number of chromatogramson the computer screen, and sends a graphic file to a printer to providea hard copy of the set number of chromatograms. In a working embodiment,gc_mplot.bas plotted 20 chromatograms on the computer screen beforesending a graphic file to a printer. The program gc_avg.bas first writesa text file containing the names of all files acquired on a given day.The gc_avg.bas program then sequentially averages each chromatogram toget a composite average for VOC data collected over a desired timeperiod, such as daily or weekly. Chromatogram averaging reduces noiseand smoothes the chromatographic baseline. This averaging procedure is anovel way of increasing the sensitivity for multiple averaged samples,e.g., for daily, weekly, etc., chromatogram averaging. The gc_avg.basprogram then sequentially plots each individual chromatogram on thecomputer screen in comparison to the daily average concurrently plotted.The gc_avg.bas program then saves the daily average with a file name,such as 1225.avg. This average chromatogram, due to averaging, will berelatively noise free and show the extant analyte peaks unambiguouslyrelative to the baseline. As such it may be subjected to any of a numberof chromatographic peak integration programs, including our own andcommercial ones, for accurate determination of peak beginnings and ends.These beginnings and ends may be then returned to the programintegpro.bas (see FIG. 49) as starting points in its own peak search andintegrate routine.

Certain programs have been written to prepare, for example, statisticalinformation concerning acquired data. For example, the programbaseline.bas conducts a polynomial fit to the baseline of an individualchromatogram or average chromatogram, subtracts the baseline, and thenplots and saves the baseline-subtracted chromatogram as a file name,such as 1225.bsl. Most chromatograms provided by the drawings werebaseline corrected.

Finally, commercially available programs may be used to plot thechromatograms. A working embodiment of the present apparatus used theEXCEL Microsoft program to plot the individual, averaged, orbaseline-subtracted chromatograms. Individual chromatograms can beintegrated by commercial programs or programs written for a particularapplication. For example, the commercially available programCHROMPERFECT can be used to integrate chromatograms.

18. Quantification of Analyte Concentrations from Chromatograms

Fully automated Pneumatic Focusing gas chromatography as described heregenerates huge amounts of raw data. For instance, one automatedinstrument has run for over 1 year measuring Portland's air pollutionand generating 40 or so chromatograms per day. This representsapproximately 14,000 chromatograms per year per column. Anotherinstrument utilizes two columns. Several computer programs arecommercially available for integration of GC peak areas forquantification of analytes, and the following have been used:

-   -   1. Chrom Perfect    -   2. Peak Simple    -   3. Peak Fit

While these programs are well written and quite useful, none areadequate to process the huge volume of data produced by automatedPneumatic Focusing gas chromatography. The reason for this is that eachof these programs is geared to significant user intervention in thedetermination of the beginning and end of peaks, split peaks, etc. as anecessary prerequisite for area integration. All these programsnecessarily allow for user override of computer selected peak beginningsand ends. However, none allow the easy application of user selections tosubsequent chromatograms, which are frequently quite similar.Consequently we have written a prototype integration programIntegpro.bas (FIG. 19) in the basic language. This program initiallyapproaches a set of chromatograms differently from commercial programswhich attempt to quantify all peaks in a given chromatogram.Integpro.bas rather focuses on a single peak which will then appear in apotentially very large number of similar chromatograms. Thus, oncerecognition and integration of a given analyte peak is optimized, theprogram can process without significant human intervention a largenumber of chromatograms. An example of the output of a single programrecognition and integration is shown in FIG. 20. Integpro.bas displaysand integrates subsequent chromatograms in rapid order. An operator mayobserve this display (if necessary or desired) and adjust ‘standard’parameters as desired to optimize correct integration. Once a givenanalyte's peak is successfully integrated the program then moves toanother peak. This program, once optimized for a large number of peaks,can successfully recognize and integrate all peaks in a givenchromatogram for realtime determination of all analyte peaks in a givenchromatogram. Output from Integrpo.bas is shown in FIG. 20. Thehorizontal axis represents reading number in a single chromatogram.Sample number 28 is being processed. Curve B is being processed, a shortportion of chromatogram 28. Peak C is being integrated note the baselinedrawn by the program. Concurrently the program plots a continuingconcentration graph of the concentration corresponding to peak “C” asmeasured in all previous chromatogram.

19. Identifying Chromatogram Peaks

Once a chromatogram is obtained, peaks are identified that correspond toanalytes of interest. Individual peaks in the chromatograms areidentified in several ways including, without limitation:

1. Using sample VOC chromatograms, available commercially, which giveanalyte elution order;

2. Spiking samples with reference VOC compounds. For example, airsamples have been selectively spiked with reference VOC compounds ofknown identity. Examples of reference VOC compounds include, but are notlimited to, individual alkanes, alkenes, etc. See Tables 1 and 2 above.

3. The pneumatically focused chromatograph may be connected to otherinstruments used for chemical identification, such as massspectrometers. By connecting the chromatograph to a mass spectrometer,the molecular weight, fragmentation pattern and presumably the identityof compounds corresponding to each peak, may be identified as it elutesfrom the column using standard gc/ms procedures. For GC/MS applications,the sample exiting from the valve is split to the MS and otherdetectors, or the excess discarded, or the STP gas flow rate is droppedto 1-2 cc/minute by computer controlled decrease in carrier pressure andopening of the flow control valve as described above. A person ofordinary skill in the art is familiar with GC/MS identification ofunknown VOCs and other compounds.

It is not necessary to use Pneumatic Focusing itself to determine peakidentities in a PFGC. Thus if the quantity of an unknown analytedelivered to a mass spectrometer is below such instrument's detectionlimit, unknown compounds discovered in PFGC may still be identified. Tothis end a PFGC may also incorporate into the sample loop or separatelya standard ‘freeze-out loop’. Such loop would be used in standardcryogenic focusing to capture and deliver to the GC/MS instrument alarger quantity of target analytes in case such concentrations deliveredby the Pneumatic Focusing technique remains below the detection limit ofthe mass spectrometer. Identification of these analytes then may becarried out (assuming the same or a similar column is used) in astandard fashion. Once unknown compounds with known retention times areidentified using standard procedures, these retention times will betransferred to all PFGCs using the same column and temperature/pressureprograms.

20. Quantifying Amounts of Individual Compounds on Chromatograms

Individual peaks (i.e., compounds) are quantified in one or more of thefollowing ways:

1. Internal reference standards, such as those listed in Tables 1 and 2,may be added at known concentrations to a sample, such as a sample airvolume. This method is known to those skilled in the art as “knownaddition,” and is exact for each compound. In the rest of the methods,previously measured or known per-carbon responses of individual VOCcompounds are applied to each individual peak compared to one of theinternal standards.

2. For air analysis, the methane peak can be used as an internalstandard for quantifying the amount of other compounds on achromatogram. This is because the concentration of methane is relativelyconstant at about 1.8 ppm for all but the most polluted air samples.Thus, areas of individual peaks can be compared to the area of themethane peak area for that same chromatogram to determine the amount ofa compound corresponding to a particular peak. Methane forms anexcellent internal standard for many atmospheric sampling situations inwhich air is not too highly polluted. Such is the case in FIG. 21 whichshows the methane concentration measured over a several day period aspart of atmospheric sampling. Note that the methane peak area variesonly slightly except when the oxygen cylinder for the flame was changed,(about sample 96) in spite of considerable variations in atmosphericpollutant concentrations. Thus normalizing each pollutant peak area tothe methane peak area, which represents 1.8 ppm will make correction forFID response. A sample calculation may be shown. Say, for instance thearea under a methane peak was 1,100 units and the area under a targetanalyte peak was 11 units. Typically methane is attenuated 10× relativeto other analyte peaks due to its high concentration. Then the targetanalyte concentration would be given by:

-   -   11/1100*1.8 ppmC/10=0.0018 ppmC=1.8 ppbC. If the target analyte        were propane C₃H₈ then its concentration would be equivalent to        1.8 pppC/3=0.9 ppb=900 ppt.

3. (Methane is slowly varying seasonally and yearly on the order of 1%or so. If necessary this variation may taken into account in acalibration procedure). Methane is an abundant pollutant from autoexhaust so that in areas with very high automobile traffic (such as LosAngeles) the variability of methane may be significant but its use as aninternal standard can still prevent gross errors in instrumentcalibration. Methane would not be a suitable internal standard forbreath analysis, since humans produce varying amounts of methanemetabolically. In this case an internal standard may be employed asdescribed previously and next.

4. An internal standard may be added to the carrier gas, such as any VOCcompound not normally present in the sample and chosen to elute in aregion of the chromatogram where no other analytes are presented. Thisinternal standard is prevented from stratifying in the carrier gascylinder by, for example, placing a small heater at the cylinder bottom,which causes continuous convective air movement within the cylinder.This internal standard will, of course, always be entering thechromatograph, but can be focused thermally at the column head so thatit elutes to form a quantitative peak upon column temperatureprogramming. The quantity of internal standard collected at the columnhead, and hence the precision and reproducibility of the calibration, isdependent upon exactly reproduced column hold and programming times. Inlaboratory operation such internal standards at not practical. In fullyautomated Pneumatic Focusing gas chromatography they may be routinelyemployed.

5. An additional standard can be added to the carrier gas separately bya gaseous permeation device of standard design.

6. Gas from a reference compressed gas cylinder containing variousinternal standards may be periodically injected onto the GC column undercomputer control instead of an ambient air sample.

21. Injection Details

In order to maximize resolution and shorten analysis time, the sampleshould be injected onto a chromatographic column in a minimum of time.Pneumatic Focusing allows the injection of a large quantity of sample ina minimum time. It is further advantageous that the sample should beinjected as a ‘plug’ with a minimum of ‘broadening’ at the edges. Suchbroadening is produced by turbulent or molecular diffusion into thesample plug by the focusing or carrier gas in the case of pneumaticinjection from a sample loop. For instance with the setup described inFIG. 1, when the multiport valve is switched, several processes occur.

1. The carrier gas currently passing through the column backflows intothe ‘downstream’ end of the sample loop. This results in columndepressurization and dilution of the sample near the downstream end ofthe loop and produces a broadened chromatographic detector output.

2. At the upstream end of the loop, the focusing gas mixes turbulentlywith the sample gas as well, also producing a sample gas plug broadenedat the edge. Such mixing is worsened in wider bore sample loops.

Such Broadening can be Minimized by at Least Two Approaches

1. Rather than using a single multiport valve, which switches all portssimultaneously, use several individual ‘3-way’ valves, which switchunder computer control at slightly different times. For instance usingcontroller 2202 in FIG. 22, valve 1 (2202) switches to isolate thesample pump, valve 2 (2204) switches to focus the sample up to valve 3(2206), meanwhile maintaining column pressure. Finally, after anappropriate time (e.g. several seconds) v3 injects the sample onto thecolumn. This approach minimizes backflow from the column into the sampleloop, but turbulent mixing may still occur at the upstream end of thesample loop. This mixing can be combated either by the use of apneumatic piston (described elsewhere) or by curtailing the injectionbefore the tail end (turbulently mixed region) of the sample isinjected. This can be done under computer control.

2. A multiport valve may still be used with minimal turbulent mixingusing appropriate check valves, which have been designed for thispurpose. These check valves consist (as is customary) of a sphericalobject (beebee) of appropriate composition (e.g. metal or plastic) whichwhen forced in one direction forms a seal, but in the opposite directionallows gas passage. We have designed inexpensive but highly efficientcheck valves using simple materials. In one manifestation a small springis held in a piece of tubing by swaging a ferrule around it or othermeans. This spring allows passage of gas past the beebee and through thespring. In the other direction another swaged ferrule stops beebeepassage, effectively stopping flow. This check valve can preventbackflow of the Pneumatic Focusing gas (e.g. helium) into the sampleline from a chromatographic column. In another application we havemodified a standard ‘Swagelok’ fitting to perform a check function whilemaintaining its fluid connectivity between two pieces of tubing bydrilling axially into the fitting to enlarge a region to accept thebeebee and then transversely through the fitting (FIG. 5) for insertionof a small wire. A beebee is placed into the drilled out region of thefitting, and a small wire is inserted through the drilled hole andsoldered or epoxied place in a leak-free fashion. The wire stops thebeebee and allows flow in one direction, while in the opposite directionthe beebee stops flow when it encounters the internal surface of themodified Swagelok fitting. This check valve can prevent backflow of thecolumn carrier gas (helium) into the sample loop. Such valves functionmore simply and more appropriately than any commercial valves we haveencountered.

Mixing of the Pneumatic Focusing gas with the sample may be eliminatedwith a device referred to as a ‘pneumatic piston’. This device(illustrated in FIG. 23) is expanded and driven by the compression gasand in so doing expands and compresses the sample gas into the GCcolumn, spectrometric cell, etc. Such a pneumatic piston may be formedfrom any suitable material. For instance Rulon J (sold by Small Parts,Inc. Miami Lakes Fla.). Rulon J is a plastic which according to theSmall Parts 2000 catalogue p. 144 was expressly developed to run againstsoft materials such as brass, type 318 stainless steel, aluminum, zinc,plastics and other materials which are worn rapidly by existing filledPTFE (Teflon) compounds. In the case of chromatography, oncepressurization of the gas sample contained in the sample loop hasreached the column pressure, the compression gas via the pneumaticpiston will continue to force sample into the column at the overall flowrate as determined by the downstream flow restriction valve. Since thisflow is know by experience, computer control of the valve switching canthereby determine the sample size injected to the column. For instance,in air monitoring, if the air is relatively clean a relatively largesample should be injected. If the air is polluted, a smaller sample maybe injected to improve resolution and minimize detector saturation. Thussample size may be completely controlled by the computer which measuresconcentrations in the previous sample and adjusts the next sample sizeaccordingly. Actual sample size can be approximately determined bycomputer timing and more accurately determined (if desired) by aninternal standard already present in or added to the sample stream, forinstance by the methane peak area for atmospheric pollution analysis.

V. Pneumatic Focusing Thermodynamic Details

Fundamental thermodynamics of phase transitions, specific heat and heattransfer govern the details of Pneumatic Focusing. When a gas iscompressed it heats as pressure-volume work is done on the gas. As thegas heats, it transfers heat to the surrounding containment vessel. Thetime/temperature profile of the gas depends upon the relative rates ofcompression and heat transfer. Concurrently, compression may causecondensable vapors (especially water vapor) to exceed its saturationvapor pressure at the pneumatic focused temperature. Thissupersaturation will cause water to seek the condensed phase. Details ofthis process will depend upon preexisting condensation nuclei in thesample (which may be removed by filtration if desired), the size of thecompression chamber, turbulence induced by compression, and the rate ofcompression. This process, especially as it may involve turbulence, isquite complex and difficult of quantitative numerical modeling.Maintaining the compressing gas at a temperature, which will be abovethe condensation point for the ultimate pressure ratio achieved, maycontrol condensation. Alternately, if it is desired to remove water fromthe sample for subsequent analysis, such water may be removed either byallowing aerosol formation/growth and subsequent filtration, or byinducing condensation on surfaces (cooled surfaces, for instance) fromwhich water can be later treated as desired. Once water is collected byeither method it may be either reevaporated by the carrier gas in achromatographic application and transferred to the same or a differentcolumn from the noncondensables, or it may be allowed to run/drip intoanother chamber for subsequent spectrometric analysis or injection intoanother chromatographic column or chromatograph (e.g. a pH meter, then aliquid chromatograph, etc.). In the case of water condensation, polarcompounds may themselves be included in the condensed water, even ifthey do not themselves exceed their 100% saturation pressure, due tovapor pressure lowering as in Henry's Law. These polar compounds wouldthen be analyzed with the ‘water fraction’. Examples of compounds to befound in the water fraction in atmospheric sampling might be methanol,ethanol, acetone, etc. Depending upon their Henry's Law coefficients atthe applicable temperature these polar compounds may partition betweenthe condensed and gas phases and be quantified in both. Details of suchpartitioning are familiar to persons experienced in thermodynamics andare described in detail elsewhere herein.

VI. Water in Chromatographed Systems

Some columns in chromatography (gas or liquid) are either harmed by thepresence of significant water or have their performance impeded, such asthrough the variation of retention times. As an example, the RT-aluminacolumns used in disclosed embodiments for VOC analysis are verysensitive to water vapor in the sample. This water vapor control isideal for analysis of nonpolar VOCs. However, if polar compounds (e.g.alcohols, aldehydes, ketones, etc.) are to be analyzed then they mustobviously be injected onto the column with the rest of the sample. Thismay involve injection of significant quantities of water vapor. On somecolumns this presents no problem. On an alumina VOC column, however,retention time variation may occur if the correct approach is notemployed. An abrupt rise in the baseline towards the end of thechromatogram is due to water ‘breakthrough’ into the FID. If significantpolar VOC compounds are present in the sample they often are ‘pushedthrough’ by the water producing a large conglomerate peak. After waterpasses into the detector, subsequent retention times on that sample maybe variable. However, they can be prevented from varying on subsequentsamples if the column is maintained a sufficiently long time at itshighest temperature before cooling for the next sample injection. Thismay require operating the column for a significant length of time (e.g.5-10 min) at this temperature even though no analyte components areeluting. If water is too much of a problem (e.g. as with aluminacolumns) an alternate column (e.g. the J&W ‘Gas Pro’ column may be used.This column has greatly reduced water sensitivity with somewhat lessdesirable separatory properties).

V. Using Pneumatic Focusing to Chromatographically Analyze Gas Samples

The apparatus described above can be used in a number ways to focus andanalyze gas samples. One embodiment of the present system used a samplecollection system. A sample pump is used to draw about 0.1-5.0 litersper minute into a sample line. A TEFLON sample line was used in aworking embodiment. This sample line was then connected to a collectioncoil, such as the ⅛ inch collection coil described above. Flow of thecollected sample is directed by the Valco multiport valve discussedabove. While the system is in sampling mode, the pump draws air samplesfrom ambient air through the valve and into the collection coil.Meanwhile, the carrier gas, such as a helium carrier gas, goes directlythrough the valve and onto the column. Periodically, such as about every40 minutes and upon completion of the elution/analysis of the previoussample, the control computer switches the valve, and the helium carriergas is diverted to pass through the collection coil. The valve remainsin this position so that the carrier gas is compressing (pneumaticallyfocusing) the gas sample and carrying it onto the column. The length oftime that the carrier gas is diverted through the collection coil is animportant consideration. Empirically, it has been determined that fornonpolar, water-insoluble analytes analyzed on a water-sensitive aluminacolumn, this time should be just sufficient to allow methane in thesample to enter the column. As soon as the methane peak is on thecolumn, then the valve is switched back to sampling mode. In thismanifestation the sample volume and hence the resultant analyte signalresponse is determined by the volume of the sample loop-in this case 40cc. By this timing sequence, condensed water vapor from the compressedsample can be almost entirely prevented from entering the column.Alternately, with water-soluble, polar analytes, the water may beprevented from condensing by elevated temperatures or be reevaporatedinto the carrier gas so that it all enters the separatory column, asdescribed elsewhere.

Sometimes when the concentration of a particular analyte is low,baseline noise is sufficient to mask the presence of analyte peaks. Thiscan be mitigated by averaging individual detector readings or byconcurrent or post-processing digital signal processing of the data fora single chromatogram. As part of this new technology chromatograms havebeen averaged over some pre-selected period of time, such as daily. Byaveraging the data, a stable baseline can be generated with greater peakmeasurement precision. Furthermore, the analyte retention times sodetermined may be fed back into the program Integpro.bas which then usesthem to measure the areas under individual peaks which are not soclearly defined due to poorer signal-to-noise ratios on an individualchromatogram relative to the averaged chromatogram.

VI. EXAMPLES

The following examples are provided to exemplify certain features ofvarious methods and apparatuses. A person of skill in the art willrecognize that the invention is not limited to those particular featuresexemplified.

Example 1

This example concerns a method for continuously monitoring air qualityusing a pneumatically focused gas chromatography (PFGC) apparatus andmethod. An apparatus as described above, capable of pneumaticallyfocusing to pressures of about 100 to about 500 psi was provided. Thechromatograph was placed in automatic mode so that it was continuouslysampling ambient air. Ambient air samples were collected and analyzedapproximately every 40 minutes using the sampling system describedabove. For this particular example, the TEFLON collection tube waspassed through the roof so that ambient air could be drawn into the tubeusing the sampling pump. The TEFLON tube was connected to an ⅛″ coiledcopper tubing, approximately 50 feet in length through an 8-port Valcorotary valve. With the system in sampling mode, the copper tubingcontinuously receives gaseous sample that is drawn into the coppertubing via the TEFLON tube as a result of the sampling pump's action.The copper tube served to destroy ozone in the air sample and preventits reaction with alkene VOCs during Pneumatic Focusing. Collectedsamples periodically were injected via Pneumatic Focusing onto a column.In this embodiment the chromatogram took approximately 33 minutes with a7 minute over cool down period for a total sampling period of 40minutes.

A system as described in this Example 1 has been continuously operatingfor >12 months collecting ambient air samples and providingchromatograms of each analyzed sample. FIG. 24 provides a series of suchchromatograms that have been prepared in the manner described in thisexample. FIG. 26 is one chromatogram of the plural chromatogramsprovided by FIG. 24 and FIG. 25 is an averaged chromatogram as preparedfor the 20 plural chromatograms of FIG. 24. FIGS. 24, 25 and 26 showthat a continuous method for collecting and sampling ambient air can bepracticed using Pneumatic Focusing and the apparatus described above,without having to cryofocus or absorbent-focus the ambient air sampleprior to injection on the GC column. In this embodiment, sample analytesdo not leave the gas phase until they begin the adsorption/desorptioncycle within the chromatographic column, which individually resolvesthem from one another and then quantifies each in the FID. Theseindividual chromatograms were then subsequently integrated with theprogram Integpro.bas described elsewhere herein. They are discussedfurther in a later example.

Example 2

A second embodiment of an apparatus has been used for continuouslysampling ambient air. This second embodiment works in substantially thesame manner as that described in the preceding paragraphs except thatthe second embodiment included 2 separatory columns and two samplecollection loops. One such separatory column is suitable for non-polarVOC compounds (Restek RT Alumina 60 m×0.32 mm id Serial number 183143)while the other is suitable for polar OVOC compounds (Supelcowax-10fused silica capillary column serial #15702-10 60 m×0.32 mm id×1.0 umfilm thickness). Typical chromatographic results are shown in FIG. 27.In both these manifestations the volume of air drawn into the coppertubing is the sample volume for Pneumatic Focusing, and subsequent GCanalysis. Thus, the sample size is determined by the interior volume ofthe sample coil.

Example 3

This example illustrates injection of a varying size ambient air samplefrom a sample loop which consisted of 50′ or ¼″ id copper tubing. Thesample loop of example 1 was replaced with a the larger diameter columnjust described. This allows for the injection of up to 10× largersamples. The interior volume of the ⅛″ sample loops is approximately 40cc while the larger sample loop is approximately 500 cc in volume. Whenoperated in the same mode as in example 1, the entire sample loop volumewas injected. Under these conditions, water removal was not assuccessful as in Example 1 with the ⅛″ sample loop and retention timesshow some variability after water eluted from the chromatographiccolumn. In variable volume injection the program GC.bas was modifiedslightly to switch the sample valve back into air-sample mode at earlierand earlier times thereby terminating sample transfer to thechromatographic column with a resultant smaller sample volume injected.This experiment showed that injection of 10× larger sample volumeresults as expected in 10× larger peaks and 10× greater sensitivity.However, also as expected, resolution of the earlier eluting compoundsis degraded since Pneumatic Focusing pressure was not increased ininverse proportion to the sample size. This degradation in resolutioncould be remedied by using higher Pneumatic Focusing pressures, notperformed in these experiments.

Example 4

This example illustrates the degree of Pneumatic Focusing that occurswith increasing pressure. A dilute gasoline vapor sample was prepared byevaporating about 0.000001 liter liquid gasoline into 847 liters of air.This sample was then analyzed chromatographically while varying thedegree of Pneumatic Focusing. The pressures used to generate the datafor this example were 200 psi, 250 psi, 350 psi and 400 psi. For thisexample, the flow/pressure control valve was not adjusted. As a result,the resolved peaks move forward on the chromatograms with increasingpressure due to faster column flow rate at higher Pneumatic Focusingpressures.

FIGS. 28-32 are chromatograms of data collected at each pressureindicated above. The chromatograms are shown to the same vertical andhorizontal scale. VOC components decreased significantly inconcentration during this 5-hour experiment due to continuing dilutionof the air sample.

By comparing FIGS. 28-32, the effects of increasing Pneumatic Focusingon the sensitivity and noise level are clear. Larger peaks just barelydiscernible in the chromatograms with the lowest pressures become muchmore discernible as the pressure increases. Noise levels are high inFIG. 28, which is at 200 psi. This may be due to flow instabilitiesthrough the pressure-regulating valve. Noise levels are much less in therest of the chromatograms of FIGS. 29-32. Resolution of peaks occurs forcertain compounds as the pressure increases. For example, a trio ofpeaks appears at approximately 10,900 reading numbers in FIG. 29. Thissame trio of peaks (which appear at about 10,500 reading numbers) ismuch better resolved in FIG. 31, collected at 400 psi. Thus, the data ofFIGS. 28-31 shows that Pneumatic Focusing provides significant benefitsfor resolving and quantifying analytes in gaseous samples. These samplescould have been pneumatically focused to even higher pressures withcontinuing improvement in sensitivity but such high pressures were notemployed in this particular prototype instrument. Such limitation is notgenerally a limitation in Pneumatic Focusing with suitably designedapparatus.

Example 5

This example concerns gasoline vapor chromatograms made at pressures of500 psi and 900 psi using a sample comprising 0.000001 liter liquidgasoline evaporated into 847 liters of air. Specifically, thesechromatograms were taken at:

-   -   a. 500 psi, 30 standard cubic centimeters/minute;    -   b. 900 psi, 30 standard cubic centimeters/minute;    -   c. 900 psi, ˜40 standard cubic centimeters/minute; and    -   d. 900 psi, ˜standard cubic centimeters/minute.

Linear flow was adjusted with the downstream valve to be about 30standard cubic centimeters/minute in cases (a) and (b) to compare theeffects of varying pressure and maintaining flow rate. These twochromatograms are shown in FIGS. 32 and 33. By comparing FIGS. 32 and 33it can be seen that superior resolution is achieved for the peakseluting between reading numbers 4,600 to 5,200 at 900 psi versus 500psi. This is because of greater Pneumatic Focusing and narrowerbandwidth occurs upon injection onto the separatory column at theincreased pressure.

Pressures were maintained constant and linear flow rates were changed toinvestigate the effects of linear flow rate at a constant pressure onresolution. For example, by comparing FIG. 34 with FIG. 35 one candetermine that the resolution is degraded even at the same columnpressure. This likely is because a faster linear velocity preventsequilibration of the analytes with the column walls.

The elution time of FIG. 35 is much shorter than the elution time ofFIG. 32 because of the higher flow rate at the same valve setting. Thepeak between reading numbers 4,000 and 5,000 is moved earlier in timeand is better resolved than in FIG. 32, but not as well as in FIG. 34.FIG. 35 terminates early because the high flow rate carrier gasextinguished the flame at reading ˜6800 reading number.

In all chromatograms of FIGS. 32-35 the tallest peak eluting between6,000 and 7,000 has identical shapes (full width at half height). Thisindicates that this analyte is focused by concentration at the columnhead, independent of the carrier focusing pressure.

Persons familiar with chromatography will realize that resolution andanalysis time are determined by balancing column pressure, linear flowrate, temperature, column length and diameter to name a fewchromatographic parameters. FIGS. 32-25 indicate that in pneumaticallyfocused chromatography, computer-controlled variations in columnpressure, flow rate, and temperature can be optimized to suit the needsof a particular separation and quantification, just as in other types ofchromatography.

The data discussed in this example was collected over a period of about5 hours, drawing sample from a test vessel. Sample withdrawal over timedecreased the concentration of the gasoline components, and their signalin the chromatographic system decreased as well. All chromatograms ofFIGS. 32-35 have been normalized to constant peak height. This explainsthe variation in the relative noise in the baseline.

Example 6

This example describes and illustrates the effect of chromatogramaveraging. Air samples were continuously taken in Portland, Oreg.,during a stormy period where wind speeds varied from about 30 miles perhour to about 80 miles per hour. The air sampled represents backgroundPacific Ocean air rapidly transported from the Oregon Coast to thePortland area, a distance of 100-200 miles. This air is quite clean, asevidenced by the virtual absence of a toluene peak in FIGS. 36-37.Toluene, often the most prevalent VOC in automobile fuel, normally isone of the most abundant VOCs in Portland Air. See FIG. 38.

-   -   a. FIG. 36 is a chromatogram taken in the middle of the        windstorm.    -   b. FIG. 37 is an average of 10 chromatograms taken before and        after the chromatogram shown in FIG. 36.    -   c. FIG. 38 is an average of 37 typical chromatograms of        Portland, Oreg.'s polluted air for reference to FIGS. 36 and 37.        By comparing FIG. 36 with FIGS. 37 and 38, it can be seen that        chromatogram averaging improves the signal-to-noise ratio.        Chromatogram averaging also increases the detection limit for        individual VOCs by about a factor of 3, which is consistent with        the appropriate square root of sample number statistical theory.

The methane peak has been attenuated by 1000× relative to the rest ofthe chromatogram in FIG. 36 and 37, but only by 100× in FIG. 38. In allbut the most polluted atmospheres, methane (CH4) is present at about 1.8ppm. Thus, in FIGS. 36 and 37, equal areas on the rest of thechromatogram represent about 1.8 ppb carbon atoms (e.g., for hexaneC6H14, an equal area would be 1.8 ppb C/6 or 300 ppt compound. Thedetection limit on the averaged chromatograms of FIGS. 37 and 38 isabout 10-20 ppt for hexane without any further digital signalprocessing.

Example 7

This example describes using Pneumatic Focusing to concentrate andanalyze analytes in gas exhalations of human subjects or patients.Although it is possible for a patient to breath directly into a sampleloop, the ⅛ inch sample loops present significant flow resistance. Wehave designed a breath sampling device to overcome this difficulty. Thesampling device, shown in FIG. 39, consists of a commercially available100 cc ground glass plunger equipped syringe. A 4-way valve has twopositions:

1. Sampling mode. In this position the sample pump purges room airthrough the sample loop (to remove adsorbents from previous samples) andthe sampling syringe is connected to the breath sample line. In thismode the subject is given an individual breathing tube (sterile) whichis then connected to the sample line. The patient breaths through thistubing, thereby inflating the syringe with 100 cc breath air. Greatestsensitivity and reproducibility is obtained in this breath sample if thesubject exhales the last 100 cc of breath air that she can convenientlyprovide. This air has been in most intimate contact with blood vesselsthrough the alveoli and contains the greatest (equilibrated)concentrations of metabolites, in contrast with the tidal lung air,which has made little blood contact. In this example the 100 cc samplevolume is suitable to fill the two 40 cc sample loops.

2. Injection mode. When the syringe reaches its uppermost, ‘full’position, the 4-way valve is switched to the inject mode. In this modethe syringe containing the breath sample is fluidly connected to thesample loops and the breath sample is pulled by the sample pump throughthe sample loop. Just as the syringe reaches the lowest ‘empty’position, the computer is triggered to pneumatically focus the breathsamples in the two sample loops into the chromatograph. In this examplemanual valve switching is employed. The breath sample is obtained inabout 10-20 seconds and the sample pump requires 20-30 seconds to pullthe sample into the sample loop. Pneumatic Focusing and injection intothe chromatograph takes approximately an additional minute. The firstVOC to elute from the column end then emerges about 2 additional minuteslater. Remaining VOC and OVOC compounds emerge from their respectivecolumns and are quantified by the respective FIDs as is normal inchromatography. This breath sampling device has the advantage that thesyringe walls are only exposed to the breath sample for a brief period.This minimizes loss of condensable components in the current breathsample or addition of undesired components remaining from a previoussubject. Additionally, the sample loops are purged with room air (or anyother desired) gas during sample analysis, also minimizing carryover ofadsorbed breath components from previous subjects.

3. The valve switching was automated so that it is completely run by thecomputer. The only user intervention is to push a single button on thechromatogram to inform the machine that a breath sample is to be taken(FIG. 39).

Breath Analysis System

This system allows the GC to automatically process a breath sample bypressing a button and exhaling into the breath intake tube whenprompted. Feedback allows the computer to acknowledge that a breathsample is being induced so that it may adjust sensitivity settings andappropriately annotate the file where it writes the data. If the systemexpects a breath sample, but does not receive one in a proper timeperiod, then it will reset itself and continue with normal automaticoperation sample b cal air.

Structure

The syringe is suspended within a chassis comprised of three equallyspaced columns between a top and bottom plate. Peg holes in the columnallow for the height of the syringe and top plate to be adjusted asnecessary. The syringe and piston act as an expanding chamber to collectthe breath sample. Switches at the top and bottom of the piston's rangeof motion allow the system to recognize the completion of the varioussteps in the breath analysis intake cycle. As the steps are completed,the system opens and shuts two electric solenoid valves to properlydirect the breath sample as it's collected and processed.

Operation

Normal analysis of atmospheric impurities in local ov air is unchangedby this system.

Breath analysis begins when the user presses the “Breath Analysis StartButton.” This causes a logic zero to be applied to the set input ofFlip-Flop 1, causing its Q output to go high. This output is sensed bythe computer as the “Wait Signal.” When the computer detects the WaitSignal it enters a sub program that adjusts the data files andsensitivity ranges to those appropriate for breath analysis. Also, thecomputer begins counting until the Wait Signal disappears after thecompletion to the breath analysis intake cycle. If the computer finishesits count before the Wait Signal disappears then the computer will issuea brief 5Vdc “Time Out” signal to the system. This Time Out signalcauses the saturation of a high gain transistor that places a logic zeroon the clock input of Flip-Flop Four. When the computer removes the TimeOut signal, Flip-Flop Four will toggle due to the collector voltage onthe transistor returning to 5Vdc. When Flip-Flop Four toggles, it placesa logic zero on the clear inputs of all the flip-flops. This causes thesystem to reset and the Wait Signal disappears. If the Wait Signal doesnot go away, then the system can tell that it is in the process of abreath sample since the piston is depressing the bottom switch.

When the wait signal appears, after pressing the start button, thechange in voltage is sensed by Flip-Flop Two's clock and causes it totoggle. This makes the second flip-flop produce 5Vdc on its Q output.This 5Vdc is applied directly to the input of a 5Vdc to 120Vac solidstate relay, forcing it to conduct since its negative input is tied toFlip-Flop Three's Q output at logic zero. When the solid state relayconducts, 120 Vac is applied to Valve One. Valve One is normallyorientated to pass only outside air, but when energized it opens a pathbetween the Breath Intake tube and the syringe. Breathing into the tubecauses the piston to rise until it closes the top switch.

When the top switch closes, a logic zero is applied to the set input ofFlip-Flop Three. This causes Flip-Flop Three's Q output to go high andstop the conduction through the relay powering valve one and cause thesolid state relay for valve two to conduct. When valve two is energized,the syringe is sealed from further gas intake and a pump draws thebreath sample into the system's sample loops. As the sample is drawnfrom the syringe, the piston lowers until it clears the bottom switch.When the bottom switch opens the clock input on Flip-Flop Four goes fromlogic zero to logic one, toggling the flip-flop, and resetting thesystem. When the system is reset, the Wait Signal drops to zero. Thecomputer then initiates the sample injection sequence and continuesaccording to its internal program.

1. One working embodiment of the breath analysis system just describedwas utilized to analyze human subjects' breath. FIG. 40 presents twochromatograms of a subject's breath taken 50 minutes apart and a thirdchromatogram of laboratory air inhaled by the subject. Each breathsample was analyzed on two columns, one for nonpolar (VOC) compounds andthe other for polar (OVOC) compounds. Thus there are 6 totalchromatograms. Major components are acetone (which appears on bothcolumns), isoprene and methanol, all concentrations virtually identicalin the subject's two breath samples; and ethanol, which differs by about10% between the two samples. All of these compounds had very smallconcentrations in laboratory air. Among the minor compounds, many butnot all were present in laboratory air and were therefore simply inhaledby the patient. Detailed analysis will be required of those minorcompounds not inhaled which could be quite important in, for instance,disease diagnosis. The methane peak is reduced 10× in all thesechromatograms and in laboratory air serves as an internal standard at1.8 ppm. Methane in this subject's breath is about twice the ambientconcentration. A breath sample from another subject is compared withlaboratory air in FIG. 41. Major components are the same as FIG. 40,except for methanol which far exceeds the ethanol concentration. Thissubject suffers from Addison's disease. No other subjects analyzed sofar have shown this methanol/ethanol concentration inversion, butfurther analysis is required before any conclusions can be reached aboutpotential disease diagnosis. FIG. 42 compares breath samples from thesame subject as FIG. 40, in this case samples taken resting and aftervigorous exercise. Laboratory air inhaled by subject is shown as well.There are a total of 6 chromatograms, 3 each on two columns as in B1.Methanol, acetone and isoprene concentrations were unaffected byvigorous exercise. Methane and ethanol were reduced by ˜⅔ followingvigorous exercise. Minor components require further detailed analysis.FIG. 43 shows ethanol metabolism in a beer-drinking subject. Thesechromatograms were taken after drinking 3 cans of beer over 120 minutes.Laboratory air is shown as well. Samples taken 50 minutes and 1 beerapart. The nonpolar column shows only very small changes in breathcompounds. The polar column shows significant changes. Methanol,isoprene and acetone concentrations were unchanged by beer consumption.Ethanol shows large further increase after consuming 3rd beer. Noticethe appearance of several apparent metabolites, which appear beforemethanol and after ethanol and whose concentration increases with time.Finally, FIG. 44 compares breath samples from a husband and wife, heavysmokers, about 30-60 minutes after smoking. In this case the nonpolar(VOC) column shows a large number of compounds while the polar columnalso shows several compounds not present in the breath of nonsmokers.

It is clear from these examples that the most efficacious analysis ofpatients' or subjects' breath for native compounds would be to exposethe patient to air zero for a sufficient length of time that the body ispurged of extraneous compounds. Such experiments are known in the art.What is not realized is that a more efficient approach would be to carryout these breath characterization experiments in regions which naturallyhave ultra clean air so that minimal non-native VOCs, OVOCs, etc. wouldbe present. Some suitable locations would be the west coast of thePacific NW, Hawaii, etc. Such areas are exposed under correct windconditions to air which has remained over the Pacific Ocean for a longperiod and has been purged of many background compounds in naturalprocesses.

Example 8

This example concerns the absorption spectroscopy of several gasessubjected to Pneumatic Focusing in a UV/VIS absorption cell.

FIG. 49 illustrates Pneumatic Focusing of acetone in room air atfocusing pressures ranging from 15 to 600 psi.

FIG. 45 is a calibration curve based Pneumatic Focusing of acetone inFIG. 49.

FIG. 46 shows Pneumatic Focusing of acetone in room air: the lower curveat atmospheric pressure shows no discernable acetone absorption due tolow concentration. Significant absorption occurs in the middle curvefocused to 500 psi. The upper 1000 psi focusing curve is in excellentagreement with twice the 500 psi curve, indicating good linearity. Theacetone absorption band is contaminated by O4 UV absorption at the shortwavelength end. Although not required for quantification (which canoccur at longer wavelengths), this O4 absorption could be subtracted asis familiar to those experienced in spectroscopy.

FIG. 48 illustrates benzene pneumatically focused in room air withspectral interference at short wavelengths by O4 absorption. The lowercurve is at atmospheric pressure. The next curve illustrates 250 psi andthe upper curves 1,500 psi compared with 6 times the 250 psi curve. Goodlinearity in band structure at the long wavelength end although the 1500psi curve shows considerable broadening (shallower valleys) compared to6*250 psi spectrum. At 1,500 psi the short wavelength spectrum showsinteraction bands with oxygen which result in enhanced absorption anddifferent band structure.

Example 9

This example describes using Pneumatic Focusing to continuously condensewater vapor, with continuous separation of the condensed water from thepneumatically focused gas sample for separate analysis. A gaseous samplecontaining water vapor is obtained. The gaseous sample is thenpneumatically focused as described above. Condensed water iscontinuously separated from the pneumatically focused sample asillustrated in FIG. 6. Each part of the sample could be analyzedseparately. For instance (without limitation) the focused gas samplecould be directed to a gas chromatograph as described above. Thecondensed water would then be directed to another analytical device. Anillustrative delivery calculation is given here. Consider a miniaturecompressor pneumatically focusing 1 liter of ambient air per minute.Assume this sample has 1% water vapor by volume. (Saturation at STP isabout 3% so this would be about 33% RH). Compression to 45 psi wouldjust start water to condense. Pressurization to 500 psi would condensevirtually all the water vapor. Using PV=nRT, this would producen=0.01 atm*1 L/(0.082 L-atm/K-mole*298K)=4.1 e−4 mole H2O4.1 e−4 mole*18 g/mole=7.4 e−3 g H2O=7.4 e−3 ml=7.4 uL=7.4 e3 nL H2O

This is sufficient for pH and other ionic measurements bymicroelectrodes. Assume, for instance, that gaseous nitric acid waspresent at a concentration of 1 ppbV in the same liter of air. This is avery modest concentration. 1 ppb=1 e−9 atm of nitric acidn=1 e−9 atm*1 L/(0.082 L-atm/K-mole*298K)=4.1 e−11 mole=0.041 nmolenitric acid

Nitric acid is extremely water soluble and all would dissolve (seeabove) to produce a concentration of 0.041 nmole/7.4 e3 nL H2O. This isa molarity of 5.4 e−6 with a pH of 5.3-acid condensate whose pH would beeasily measured by a microelectrode described below.

This analysis could be made as the condensed water flowed continuouslypast the microelectrode which would not alter the solution. Since pHmeasurement can be made on 10 uL by commonly available microelectrodes,the averaging time of the pH measurement in Pneumatic Focusing systemwould be 1 minute. One example of a microelectrode source is LazarProducts (http://www.lazarlab.com/). Their literature states that pH maybe determined using their Micro combination pH (BNC Conn) PHR-146Belectrode. They offer numerous other electrodes for specific ions ofatmospheric interest. These electrodes can make measurements in aslittle as {fraction (1/10)} of a drop (5 uL) at a depth of 0.1 mm. Inaddition to pH, a variety of other specific ions could be determined ina nondestructive fashion as the water sample passed to anotheranalytical device such as a spectrometer cell which also performs anon-destructive analysis. Finally, the water sample could pass to a thesample inlet of a destructive device such as a Pneumatic Focusing orother gas or liquid chromatograph.

The previous considerations would apply equally if some additionalacidic material were present in the air sample in either the gas or theparticulate phase, as Pneumatic Focusing would capture all water solublematerials.

Example 10

This example demonstrates and illustrates a method for determining thedirectional distribution and emission strength of emission sourcesaround a single PFGC monitoring station. As such the method can beuseful for locating and quantifying pollution sources without referenceto emission inventories, stack monitoring, or any direct or in situanalysis. It is thus useful for confirming or denying the validity ofemission inventories which are notoriously unreliable. (Employment oftwo of more PFGCs provides a much more powerful system and is discussedin the next example).

In a proof of principle demonstration we have used PFGC to locate andquantify an intermittently operating source upwind from our PFGC. Anautomatically operating, continuous, Pneumatic Focusing analysis systemwas set up to analyze samples taken from the roof of our building. Windspeed and direction were also measured and recorded every 10 minutesusing commonly available instrumentation. Samples were continuouslyobtained about every 40 minutes, pneumatically focused and analyzed asdescribed above.

The distribution of such pollutants downwind from a source is commonlydescribed by a Gaussian Plume Model in which the pollutants diffusevertically and horizontally as they are carried downwind toward areceptor site. (See, for instance, J H Seinfeld and S N Pandis,Atmospheric Chemistry and Physics, John Wiley & Sons, 1998 pp. 880-957,especially pp. 945-47 which treats multiple source plume models).Essentially, the pollutant distribution follows a gaussian distributionboth horizontally or vertically and this gaussian half-width, standarddeviation, or other measure of dispersion increases with downwind flow.Spreading is caused by turbulent diffusion and appropriate diffusioncoefficients are available which are a function of surface structure(roughness) and wind speed. Such models are commonly employed in thefield of air pollution science and engineering and are familiar to thoseexperienced in this field. This gaussian behavior may be exploited tocharacterize pollutant emission sources as measured downwind by a singlePFGC.

FIG. 24 presents an exemplary subset of chromatograms obtained in theambient atmosphere during a period of about 10 days. As described above,FIG. 20 shows the integration of a single GC peak by Integpro.bas. FIG.48 presents concentrations of pollutants as determined with reference tothe methane concentration by the program Integpro.bas described above.Several variables are shown on this graph. The points represent winddirection as determined about every 10 minutes. The right hand axisindicates that wind was substantially from the north (360 degrees,occasionally wrapping around to zero degrees) during this period.Methane is taken constant at 1.8 ppm and drift in its concentration(shown as the continuous line in the center of the figure) is taken asdue to instrumental drift. The abrupt drop in methane response at aboutsample 97 is due to a change of cylinder gas to the FID. Pollutantconcentrations are normalized to this changing response. The remainderof the curves are a subset of individual pollutants as determined inthis study. Note that some pollutant species are identified as tochemical identity while others are currently unidentified and expressedin terms of their retention time on the GC analysis. Reference to a mapof the subject area indicated that the major pollution sources probablyoriginated in an industrial area approximately 5 miles upwind. With asingle site and no significant shift in wind direction it is notpossible to determine exactly the location of the source or the sourcestrength, since it is unknown how far the source is from the vectoredwind direction. However, it is possible to determine a lower limit tothe emission source strength by assuming it is centered directly upwindand that emissions originated in the industrial area. If the source isnot directly up wind, the maximum would not be received at the PFGCmonitoring site and the actual source rate would be larger. Thisemission source strength could be determined for each of the individualpollutants measured by PFGC assuming they all could be assigned to thesame source. In this particular situation, the emission site would haveto be located by ground truthing. Once this were done, the GaussianPlume Model could be used to quantify emission sources for eachindividual compound, assuming they originated from the same singlesource. The next example carries the analysis a step further.

Example 11

The previous description deals only with the actual pollutantconcentrations measured by PFGC. A more informative and more thoroughapproach may build upon those results. To carry out this more completeanalysis the output concentrations from the integration of each sampleby Integpro.bas is fed a Microsoft Excel spreadsheet file. These dataare then output as a text file and fed to the program UNMIX describedpreviously. Table III gives the source distributions as determined bythe program UNMIX operating on the data of Example 8.

TABLE III Compounds Source 1 Source 2 Source 3 Acetylene 0.13728 2.294860.80171 Benzene 0.08900 0.00005 0.54703 rtx#11660 0.01430 1.49792−0.00520 rtx#11456 0.00007 2.16476 0.06542 rtx#10970 0.00620 0.356920.00352 T-2Hexene 0.01759 0.53155 0.03835 rtx#10345 0.16815 −0.055461.27916 rtx#9750 0.06894 1.68992 0.51805 rtx#9486 0.23377 8.802211.12259 rtx#8360 0.28109 −0.19686 2.58218 Pentane 0.15852 0.001441.45255 rtx#9229 0.00306 0.50905 0.03779 Butane 0.18095 −0.15603 1.93525Isobutane/Propene 0.11334 −0.01207 0.74688 MysteryBump6862 0.041620.85410 0.17550 Toluene 0.30667 0.04077 1.82316 Hexane 0.07787 −0.002980.52961 Octane −0.00465 0.47018 0.09961 rtx#11100 0.01564 0.005970.10944 rtx#11358 0.44013 −0.00115 0.04843 rtx#11225 0.01291 0.049840.14702 TOTAL 2.36244 18.84499 14.05805

The computer program UNMIX was then used to analyze the data anddetermine the distribution of emission sources upwind from the PFGCmonitoring station during this period. The program UNMIX is publiclyavailable from, for example, Ronald C. Henry, Civil EngineeringDepartment of the University of Southern California. Its use has beendescribed in: (1) R. Henry et al. “Vehicle-Related Hydrocarbon SourceCompositions from Ambient Data: The GRACE/SAFER Method”, EnvironmentalScience and Technology, 28:823-832 (1994); and (2) Henry et al.“Reported Emissions of Organic Gases are not Consistent withObservations,” Proc. Natl. Acad. Sci., 94:6596-6599 (1997); both ofwhich are incorporated herein by reference. Dr. Henry provides aoperation manual with the program.

Next, each individual sample is analyzed by least squares to determinethe contribution of each of the three sources found by UNMIX to describethe PFGC data of example 8. This analysis is not provided by UNMIX butis a form of Source Reconciliation or Chemical Mass Balance as discussedby for instance, J H Seinfeld and S N Pandis, Atmospheric Chemistry andPhysics, John Wiley & Sons, 1998 pp. 1248-58). This process, moreproperly called multiple linear regression analysis is familiar to thoseknowledgeable in statistics and is illustrated here only by example.Four sets of variables are defined. Some of these variables are unitless(e.g. % or fractions) while others are expressed in parts per billion ascarbon atoms ppbC or ppbC/min. These units are familiar to thoseexperienced in air pollution and are roughly proportional to FIDresponse as determined by the PFGC FID analysis of example 8. Thusethane C2H6 produces approximately twice the FID response of methaneCH4, hexane C6H14 produces approximately 6 times the response asmethane, etc. The four variables are

-   -   Ei emission sources: E1, E2, E3, relative units, these are found        by UNMIX    -   Pi individual pollutants: P1, P2, P3, P10 units are ppbC        measured by PFGC    -   Si individual samples analyzed: S1, S2, S3, S174 no units, just        an identifier    -   Xi source contributions to each sample Si: X1, X2, X3 ppbC/min    -   UNMIX identifies three sources: which contribute to the samples        Si.

For purposes of example assume the following array of emissions werefound by UNMIX

P1 P2 P3 E1 0.2 0.4 0.4 note that the Ei sum to unity E2 0.3 0.1 0.6 E30.2 0.3 0.5

Now the contribution of each emission source Ei to each sample Si isfound by least squares minimization. For illustrative purposes this willbe done in reverse. Assume that in S1, E1 contributed 2.0, E2contributed 7.0, and E3 contributed 5.0 ppbC total pollutants P1+P2+P3

-   -   that is, X1=2, x2=7 and x3=5 ppbC    -   Thus S1 contains        P 1 =x 1*0.2+x 2*0.4 +x 3*0.4=5.2        P 2 =x 1*0.3+x 2*0.1 +x 3*0.6=1.6        P 3=1*0.2+x 2*0.3+x 3*0.5=5.0

These three quantities (ppbC) would be the areas under the under thepeaks P1, P2, and P3 in PFGC-analyzed sample S1 as ratioed to theinternal standard methane concentration of 1.8 ppbC.

In the general case the goal is to find Xi (which would of course beunknown) from the measured values Pi. To do this the following is to beminimized:[(P 1−(x 1*0.2+x 2*0.4+x 3*0.4))^2+((P 2−(x 1*0.3+x 2*0.1+x3*0.6))^2+((P 3−(x 1*0.2+x 2*0.3+x 3*0.5)){circumflex over (0)}2]

This is a familiar problem which has a well know solution yielding thevalues of X1, X2, and X3.

Using the created emission sources here it is of course equal to zero:[(P 1−(2*0.2+7*0.4+5*0.4))^2+((P2−(2*0.3+7*0.1+5*0.6))^2+((P3−(2*0.2+7*0.3+5*0.5))^2]=0 (as defined forthis illustrative example)

Each term in the previous equation is identified with the residuals forP1, P2, and P3.

Thus in finding X1, X2, and X3 the residuals are minimized. However, ina real world case they will not equal zero because of measurement error,variation in emission rates and composition, the presence of more thanthe 3 sources found by UNMIX, errors in UNMIX, variation in winddirection, and numerous other effects. These residuals then allow agoodness of fit calculation to be made. From them may be calculated thestandard deviation, standard error of the mean, uncertainties in thecoefficients Xi, etc, as is described in any statistics book.

Once the above analysis has been performed for all samples Si, the nextstep in source location is to plot all the Xi values for each emissionsource for all the samples vs. wind direction. If the wind is variablein direction and a given source is upwind at least some of the time,this curve will produce a true maximum at the compass direction betweenthe receptor site where the PFGC is located and the individual emissionsource Ei. If the maximum is found at the extreme angle of winddirection which occurred (not a true maximum) then the source was notdirectly upwind. In this case the actual maximum may be found byextrapolation of the Gaussian Plume Model. In the event that novariation in emission source strength is seen with wind direction, thenan area source (such as traffic or vegetation) has been located.

If there is no variation in wind direction during the sampling periodthen the exact location of an individual emission source cannot beexactly located without ground truthing since the source could be offthe wind compass direction and the center of the plume is not beingencountered. In this case a lower limit emission rate could becalculated on the assumption that the source was located directly upwindin the constant wind field at a distance from ground truthing. In thissituation a map could be referred to and potential emission sourceslooked for. If a possible source is located, then application of theGaussian Plume Model will allow that source to be quantified from thecollected sample data Si.

Example 12

This example describes the location of an emission source by the processof triangulation which is allowed by employment of two or more PFGCs. Inthis manner, analyses are conducted at plural monitoring stations, forinstance in a linear, crosswind orientation downwind from an industrialarea, city, or other multiple pollutant source area. Such data couldthen be used, along with triangulation, to determine the source locationand strength of a particular measured analyte or analytes. We have notyet employed two PFGCs in the method described next, but the approach isdescribed.

Triangulation of emission sources may be accomplished (withoutlimitation) as follows.

1. Establish two or more automatic pneumatically focused gaschromatographs at several locations. These instruments could be placed,for instance, downwind from a source area, such as an industrial area,transversely oriented with the normal wind direction for the givenseason. It is by no means necessary that there be a constant winddirection. In fact, if wind direction is variable more spatialinformation may be obtained simply by segregating data into various winddirection coordinates as described in previous examples. Spacing betweeninstruments could be decided by application of the Gaussian Plume modelto determine diffusional spreading vs. downwind direction based upondistance from suspected emission sources. With variable winds in a city,for instance, placement might be chosen at random. Take samples undervarying wind, atmospheric temperature-inversion, and emission conditionsfor periods ranging from days to weeks to months.

2. Apply the program UNMIX to determine the range of emission sourcescontributing to the observed pollutant concentrations at each site byanalyzing all the data samples over selected time periods of days toweeks. This analysis should be employed to the entire data set,regardless of wind direction, and to specific subsets based upon winddirection, weekdays vs. weekends, etc. Such approaches are familiar tothose involved in study and regulations of air polution.

3. For each individual sample, determine the emission sourcescontributing to the observed total pollutant concentration at eachprecise time at each site as described in the previous example. Plotindividual absolute source contribution to each analyzed sample as winddirection as described above. With variation in wind direction, thiscurve should produce a maximum in source contribution when the specificsource is directly upwind.

4. Use the wind direction which produces a maximum absolute sourcecontribution to draw the two upwind vectors leading from all pairs(trios may be employed as well) of adjacent monitoring instruments. Asin any triangulation, these two vectors will cross at the point ofemission impacting each pair of adjacent measurement stations for theparticular wind direction and pollutant concentrations of that pair ofmeasurements.

5. Once the source location has been, determined, source strength may bedetermined from an application of the Gaussian Plume model usingdispersion parameters appropriate for the local topography and measuredwind speeds. With these given constraints, pollutant concentrations at areceptor site are simply a function of the downwind distance (known fromtriangulation) and the emission source strength, which of course may betime varying.

6. It is expected that some sources will not produce maxima in thesource contribution with wind direction, or that such maxima will bequite broad. In this case such sources represent area sources, such astraffic or vegetative emissions. These sources should have compositionswhich are currently associated with such emissions as recognized tothose familiar with air pollution.

7. It is further expected that some source vs. wind direction graphswill produce maxima at the extrema of wind direction encountered. Suchsources were never directly up wind. Their actual location may bedetermined two ways.

-   -   a. By extrapolating a Gaussian curve through the observed points        to find the maximum, or    -   b. by moving an appropriate pair of PFGC instruments in the        direction of the actual maximum.

1. There will be some uncertainty in an individual triangulation due toshifts in wind direction, variation in emission strengths orcomposition. This is to be expected. However, by averaging over allsources, all compounds, all wind directions, considerably confidence canbe built up in the sum total results of a large number oftriangulations.

2. Finally, use a standard Gaussian plume model fixed on the estimatedemission site to model the predicted pollutant concentrations atadjacent sites. Compare predicted pollutant concentrations withobserved. Perform appropriate statistical calculations.

3. Finally, if necessary or desired, move at least pairs of instrumentsin directions (closer if necessary) to suspected emissions sites forimprovement in precision and accuracy.

4. Lastly, (or even firstly) ground truth the calculations qualitativelyby visiting the suspected emission sites and by consulting emissioninventories maintained by local air pollution control districts.

Example 13

This example concerns the identification of intermittent sources whichdue to their sporadic rate of emission are not detected by thestatistical program UNMIX. Such sources might include, for instance,illegal drug synthesis labs which intermittently boil off solvents orpour them on the ground from which they evaporate. Detection of theseemissions proceeds substantially as example 8, except that such sourceswill not be identified by the program UNMIX. Rather they may be detectedby examination of the residuals determined from source distributionanalysis using the output of UNMIX. This is done by examining thebest-fit residuals calculated in the fitting procedure of item 3,example 8. These extrema in the residuals will represent occasional orintermittent sources of an individual pollutant P. These intermittentsources may then be spatially located as described in Example 8. Lastly,the exact nature of the sporadic emissions could be discussed with localpollution and law enforcement agencies.

Example 14

This example concerns the use of PFGC to locate harmful outgassingsubstances in an indoor environment. Such environments might includewithout limitation residential buildings, office buildings, factories,etc. Such outgassing substances can contribute to what is termed SickBuilding Syndrome and might include active substances such as molds andfungi and passive substances such as paint, particle board, carpets,drapes, household products, pesticides, etc. In some cases the outgassedchemical compounds may themselves be irritating and/or harmful. In othercases the detected pollutants (e.g. heptanol from bacteria) may notthemselves be harmful but may serve as indicators or surrogates for thepresence of harmful organisms which produce spores or other materialswhich are indeed harmful but which are harder to detect.

Provide a PFGC, most suitably including two columns and two detectors,one each to sample incoming and outgoing building air. Choose a pair ofseparatory columns most suitable for the range of pollutants to beencountered. Numerous manufacturers of these columns can providedetailed advice and sample chromatograms. In some cases two separatecolumns might be required to completely cover the range of targetanalytes as in the breath analysis of a previous example. In such casethe PFGC might contain 4 columns and 4 detectors. All four detectorscould be accommodated by a single A/D board. Analysis would mostbeneficially be done by attachment to the building ventilation system.One sample line draws a continuous air sample from the incoming buildingair and the other from the outgoing (exhaust) air. Carry out continuoussampling and analysis of this air for a period of days to weeks. Datataken in the outgoing (exhaust) air stream will allow human exposure tomeasured pollutants to be calculated. Comparison of these two sets ofcontinuous samples will allow the origin of all building air componentsto be assigned either to outgassing within the building or transfer fromoutdoors through the ventilation system determine sources using UNMIX.These data will allow risk assessment, liability or other litigiousissues to be settled. The data will also suggest the most effectiveremediation measures to be taken. If the pollution source is indoors andcannot be deduced from initial measurements. Then the PFGC could bededicated to monitoring individual rooms or areas of the building. Inthis case individual sample lines could be directed to separate areas tospeed the detection process.

Example 15

This example concerns the identification and quantification of commonoutgassing substances from respiratory organisms such as variousbacteria, molds, fungi, etc. such as might be present in damp buildingsprone to exhibit sick building syndrome. Obtain a culture of a suitableliving organism from a commercial source or by scraping from a buildingwhich exhibits sick building syndrome. Establish a culture medium withsuitable humidity and nutrients in an enclosed situation such as abeaker, fish tank, etc. Suspend the culture within the culture vessel ona suitable light-weight substrate that may be periodically weighed todetermine colony growth rate. Slowly pass purified, pre-humidified airthrough said culture vessel at a low volume flow rate. This rate may bechosen to establish reasonable, measurable levels of gaseous metabolicproducts. Such flow rate may be chosen from the following theoreticalcalculation familiar to those involved in the art. Consider a culturevessel volume V(L), a purge flow rate F(L/min), and an offgassing ratefor a target compound G(ng/min). These will establish a steady-stateconcentration P(ng/L)=G/F of the pollutant with the sampling time (tau)to reach (1/2.7) of equilibrium given by the residence time V/F (min).Of course offgassing rates may vary significantly with time as theculture grows. The flow response time tau represents an averaging timefor the determination of these changing offgassing rates. This abovegrowth chamber is essentially a metabolic chamber which could be appliedwithout limitation to a variety of higher organisms (including humans)whose gaseous metabolic by-products in breath and otherwise werequantitatively and continuously determined by PFGC.

Example 16

This example concerns the application of PFGC to continuous automatedanalysis of water samples. As an example, consider a river subjected tonatural and anthropogenic pollution sources. Such a moving body of waterwill continuously transport varying quantities of natural oranthropogenic pollutants past any fixed point. Concentration of suchpollutants may vary with depth in the river, river flow, season, etc.Such variations may be determined as in Example 1 by modifications ofthe PFGC described for gaseous analysis as shown in FIG. 8. To do thesemodifications one should:

1. Choose a chromatographic column which is impervious to the action ofhigh-temperature, high-pressure water vapor and which will preferablyhave a polarity such that the vaporized water sample passes throughahead of the desired analytes. Alternately, the column could pass thewater vapor subsequent to the analytes. Finally superheated water couldform the mobile phase. Water is not commonly injected ontochromatographic columns. Rather such water samples are ‘stripped’ oftheir organic components by either ‘trap and purge’ or by extraction toa hydrophobic phase. Such methods are slow, complex, expensive, andprone to artifacts and error. Appropriate columns for water injectionare not currently in widespread use. Nonetheless, such separations arepossible. See the paper “Supercritical fluids in separation science—thedreams, the reality and the future” Journal of Chromatography A 856(1999) pp. 83-115 and references contained therein. To quote from thisauthoritative source, Superheated water can also be used as a mobilephase for reversed-phase liquid chromatography (references) with both UVand fluorescence spectroscopic detection and universal FID (references).The eluent can also be buffered (ref) and the separation applied to arange of analytes including pharmaceuticals (ref). Thus water with theappropriate stationary phase can be used as an eluent. For PneumaticFocusing two situations can be envisioned:

-   -   a. A liquid water sample is automatically injected into a PFGC.        In this case water is simply the ‘native’ vehicle to transfer        the analytes (water pollutants) to the Pneumatically Focused        separatory column. Thus in this application it is only necessary        that the water not destroy the column when passing through prior        to the analytes to be separated chromatographically using any of        a variety of sub or supercritical mobile phases.    -   b. A liquid water sample is transferred directly to a liquid        chromatograph which may employ superheated water as the eluent.        This situation would duplicate the non-automated analysis        referenced in the just described J. Chromatography article.

2. Substitution of a sample loop of approximately 1 cc volume. The mostappropriate volume will be determined by experimentation. This sampleloop will perform direct river water injection into the PFGC.

3. Adjusting the sample injection block temperature to a temperaturewhich will ‘flash’ evaporate the water at high pressure upon transitthrough the sample block. Such temperature may be determined eithertheoretically (consult stream tables) and/or by experimentation withtemperature and flow rate through such sample block. Flow rate and heattransfer may be varied by the diameter of the sample inlet tube from thesample loop to the chromatographic column.

4. Said sample loop will inject the river water sample through a heatedinjection sample block (modification described above) such as is commonfor syringe injection. When the water sample passes through this heatedsample block it will be vaporized as is common in liquid injection.However, the high pressure within the PFGC will reduce the gaseous waterexpansion factor (relative to injection into a ‘normal’ gaschromatograph by a factor proportionate to the internal GC pressures.For instance, if a ‘standard’ GC uses a head pressure of 30 psi and aPFGC uses a head pressure of 300 psi this compression ratio will be afactor of 10. Essentially (and to a first order approximation) the PFGCallows a sensitivity increase (relative to a standard GC) of 10×.Correspondingly, a PF pressure of 3000 psi will allow a sensitivityincrease of 100×.

Example 17

This example, being substantially similar to Example 10, is only brieflydescribed. In this method continuous monitoring of river pollutantconcentrations is used to determine sources. Two methods (withoutlimitation) are described.

1. In this case, rather than plural PFGC instruments located atdifferent locations, on or more such instruments, containing (ifdesired) plural columns are located at a single site with sample linesrunning to different positions in the river. Typically these samplelines would have to be at a depth such as would not interfere with boattraffic.

2. Instruments are located at different downstream locations, samplingone or more transverse or depth locations within the flowing stream.

As in Example 10, choose an appropriate liquid phase transport model toanalyze such data. In particular, a series of instruments located alongthe river's course, could pick up pollution sources with much simpleranalysis than in the case of air monitoring.

Sample lines should admit no light to prevent algal growth and sampleflow should be appropriately filtered to prevent clogging. Sample flowthrough the sample loop may be continuous as in gas phase analysis orintermittent following each previous sample analysis.

Example 18

This example illustrates fluctuation in transmission of lamp intensityas determined using the apparatus of FIG. 2. No unusual fluctuationswere observed with helium. Other gases (as shown in FIG. 50) exhibitedquasi random or chaotic variation in transmission (or absorbance) whichvaried in magnitude with wavelength. When UV/VIS emitting lamp 84 inFIG. 2 was replaced with a source of visible radiation only, thesefluctuations did not occur.

Example 19

This example describes particular embodiments of pneumatic focusingsystems contained substantially within commercially available personalcomputer cases. Constructing pneumatic focusing instruments withincommercially available computer cases is an example of a more generalapproach to providing instrumentation that is both portable and lessexpensive. Modification and use of a personal computer case to house thecomponents of an analytical instrument is not solely suitable forpneumatic focusing gas chromatography.

Instruments that may be constructed within personal computer casesinclude gas chromatographs in general, pneumatic focusingspectrophotometers, gas chromatography/mass spectrometryinstrumentation, mass spectrometers, particulate detection systems,fluorescence spectrophotometers and infrared spectrophotometers. Anotherexample is an atomic absorption/atomic emission/atomic fluorescence(AA/AE/AF) spectrometer. Such an instrument may include, for example, amultiple lamp turret, a graphite furnace, and spray/flame device that isvery similar to a Flame Ionization Detector (FID) mounted within apersonal computer case. These components can easily be contained in astandard tower ATX case, server case, etc, and as the components arefurther shrunk, such as in “lab on a chip” technologies, the more the‘in a pc’ becomes a viable alternative. A suite of spectrometersincluding infrared (IR), near-infrared (NIR), x-ray, andultraviolet-visible (UV-Vis) spectrometers, as well as a fluorescencespectrometers using broadband source excitation and emissionmonochromators may be contained within a personal computer case. Variouslaser spectroscopic instruments, for example, intracavity absorption;Raman; resonance ionization, fluorescence and chemiluminescencespectrometer also may be constructed in a personal computer case.Further, various mass spectrometers, using mass detection techniquessuch as quadrupole, ion-trap (inverted quadrupole), and time-of-flightmay be housed in a personal computer case. A high pressure liquidchromatographic (HPLC) system and its associated solvent sources,pumping system, and HPLC column, would easily fit within personalcomputer cases. Similarly, an ion chromatograph (IC) would be anexcellent companion to an HPLC in a pc, and would only need a differentdetector and column. For example, a dual HPLC-IC could be constructed ina personal computer case. Other embodiments of an “instrument in a PC”include a microscope (wherein, for example, the personal computer caseis modified to include a large port for access to a sample stage;internal optics and camera chip, and a display screen, with focus,translation, and magnification controlled from a keyboard or mouse). Anion selective electrode (ISE) may be constructed in a personal computercase, and used, for example, continuously sample various ions that aretracked by regulatory agencies such as the EPA. Such an ISE/PCcombination would permit for continuous data logging and display forprocess effluents or downstream tracking of pollutants.

A case for a pneumatic focusing gas system is desired for a number orreasons, including protection of system components. Typically, suchsystems are run by external personal computers, such as laptop personalcomputers, or the systems are in large containers that contain computerprocessors. However, as demonstrated herein, all the components for apneumatic focusing gas chromatograph may be contained within acommercial personal computer case along with the components that arenormally present in a personal computer. Commercially available computercases often include a power supply, and the power supply may be used notonly to power the computer, but components of the pneumatic focusingsystem. In one embodiment, modifications to a computer case to permitintroduction of samples and to provide gases (such as FID gases, sample,and pneumatic focusing gases) were made, and the resultant instrumentincorporated all the normal functions of a personal computer as well asall the functions of a pneumatic focusing gas chromatograph, a highlydesirable combination.

A personal computer (PC) is generally contained within a personalcomputer case and contains some or all of the following computercomponents, which constitute in whole or in part what is termed a“computer.” The computer case refers to an enclosure, such as a metal orplastic enclosure, that provides or is designed to accommodate at leastsome of the following components:

-   -   1. Power Supply: A unit which plugs into wall line voltage (e.g.        110 V, 60 Hz) and provides a variety of types of electric power        to the computer and its components such as 6V and 12V DC. The        power supply is typically sold as an integral part of a computer        case.    -   2. Fan: a small device for circulating air inside the computer        case for the purpose of removing excess heat and cooling the        computer; several such fans may be employed; an alternative is a        water cooling system.    -   3. Operating System or OS: a computer program that controls the        processor. An example would be Microsoft Windows 98, 2000, etc.    -   4. Hard Drive: a magnetic storage device for permanently        storing (1) computer operating systems, (2) programs or        software, (3) data.    -   5. Mother Board: a circuit board, commonly mounted within a        computer case to which various other components are themselves        mounted.    -   6. Memory: a magnetic storage device for storing programs,        software and data while the computer is operating; also called        RAM, or random access memory. This memory refreshes or resets        itself when the computer is turned off. It is commonly mounted        on the motherboard.    -   7. Processor: the actual electronic device that operates the        computer, runs programs, and causes the various computer        components to communicate with one other. This is mounted on the        Mother Board. Example would be any of the processors        manufactured by Intel (Santa Clara, Calif.) or AMD (Sunnyvale,        Calif.).    -   8. Graphics display card, sound card, network card, etc. Control        cards for display, sound, communication with other computers,        etc. These may be separate circuit boards or ‘cards’ mounted        within the case, or their functionality may be incorporated onto        the mother board directly without requiring additional cards.    -   9. AID & D/A conversion or cards: these additional circuit        boards may be mounted within the case and allow the computer to        acquire analog or digital data from instrumentation (such as        from a GC) and to communicate with or operate instruments, such        as a GC.

As is commonly the commercial situation, computers may be purchaseddirectly from a distributor fully constituted so that they contain some,all, or more than the above components, and such a device is commonlycalled a “computer.” Alternatively, any or all of the above componentsmay be purchased separately from a distributor and the computerassembled from its component parts. This may be done by a reseller or bythe end user.

In all cases of the existing art, the computer used to run a GC isattached as a peripheral to or is contained within a case designed forthe GC. In contrast, the disclosed instrument consists of constructing aGC within a case designed to house a commercial personal computer (PC);that is, constructed within a personal computer case by modifying thecomputer case to provide, for example, inlets and outlets as necessaryto supply gases, samples etc. and to exhaust waste gases.

A wide variety of computer cases (enclosures) are available that,although not designed for the purpose, nevertheless may be used to housea wide range of analytical instrumentation in place of the specializedcases currently employed. For example, such cases may be obtained fromColorcase (Rowland Heights, Calif.) and CaseDepot (Santa Fe Springs,Calif.). Computer cases suitable for enclosing scientific instrumentssuch as pneumatic focusing gas chromatographic, include AT, BATX, ATX,MATX, LPX and microATX compatible cases (referring to theircompatibility with particular types of motherboards), and (full) tower,mid-tower, microtower, desktop, rackmount and server chassis cases(referring to their size and configurations). Particularly suitablecomputer cases are portable cases having a built-in screen, keyboard andcarrying handle. Such computer cases are available from CaseDepot (SantaFe Springs, Calif.). Additional manufacturers/suppliers of suitablecomputer cases include Antec (Fremont, Calif.), Avus (City of Industry,Calif.), Cables Unlimited (Bohemia, N.Y.), Chieftec (Fletcher, Ohio),CrazyPC (Walled Lake, Mich.), FuturePower (Glendale Heights, Ill.),Kingwin (Walnut, Calif.), Koolance (Federal Way, Wash.), pcToys(Woodinville, Wash.), Soyo Tek (Fremont, Calif.) and Zerus Hardware(Springfield, Mo.). Any of these cases may be modified to housescientific instruments. In a particular embodiment, the computer casemay also be modified to include an integral video screen, such as a5-inch video screen, available, for example, from Parts Express(Springboro, Ohio). If a small monitor is present on the computer case,an external monitor is not necessary (although one may still be employedin parallel with the incorporated 5 inch monitor), providing greaterportability for the instrument. In other particular embodiments,appropriate computer cases have a volume (based on external dimensions)of not more than 4500 in³, such as not more than 3500 in³, for example,not more than 2500 in³.

In a working embodiment, a pneumatic focusing gas chromatographic systemas previously shown in FIG. 1 was constructed within an ATX compatible,tower computer case having the outer dimensions of 20 inches by 19inches by 8 inches (volume=3040 in³). A handle was affixed to the top ofthe case.

Referring now to FIG. 51, a rear view of a computer case 5101 is shownwith a particular layout of inlet and outlet ports for sampling and gaslines that were provided by modifying the computer case. The modifiedcomputer case includes helium inlet 5102. Helium inlet 5102 was added tothe case by drilling a hole to accept a Swagelok Bulkhead UnionSS-200-61. Sample inlet 5103 was added to the PC case by drilling a holeto accept a Swagelok Bulkhead Union B-400-61. Hydrogen inlet 5104, likehelium carrier gas inlet 5102 was added by drilling a hole to accept aSwagelok Bulkhead Union B-200-61, as was oxygen inlet 5105.

FIG. 52 shows a side cut-away view of computer case 5101 modified toenclose the major components of a pneumatic focusing gas chromatographas illustrated previously in FIG. 1. FID assembly 5202 was added to thePC case by drilling vent holes through the top panel and cutting awaythe bulkhead side wall of the PC case to allow the FID assembly toeasily slide into place when mounted atop oven unit 5220. Within theoven unit 5220 is column assembly 5203, and resistive heating element5204. Resistive heating element is electrically connected to circuitassembly 5209 through resistive heating element power supply terminals5219 (electrical connections not shown).

Column assembly 5203 is fluidly connected between 6-port gas valve 5216(Swagelok Ball Valve SS-4346FS2) (connection not shown) and FID assembly5202. 6-port gas valve 5216 also is fluidly connected to sample inlet5103 of FIG. 51 through a sample loop that is located in the sample loopassembly 5214 (loop not explicitly shown) Helium carrier gas inlet 5102of FIG. 51 is also fluidly connected to 6-port gas valve 5216 (notshown). FIG. 1 illustrates the connections to 6-port gas valve 5216 thatare not explicitly shown in FIG. 52. Although not shown in FIG. 52, aflow restrictor valve is present in the conduit that extends betweencolumn assembly 5203 and FID assembly 5202, as was shown in FIG. 1.

Below oven unit 5220 are mounted removable media (e.g. CD-ROM or floppydisk drive) data storage device 5205 and non-removable media (i.e.hard-drive) data storage device 5206. Below the data storage devices5205 and 5206 is a circuit assembly 5207 for automation of 6-port gasvalve 5216, which was added to the PC case by drilling mounting holesfor a circuit enclosure box.

Actuation motor 5208 for controlling 6-port gas valve 5216 was added tothe PC case by drilling mounting holes to attach it to the PC case.Motor/valve shaft coupler 5217, a custom fabricated part used to connectthe motor and valve shafts. Motor/Valve Bracket Assembly 5218 is acustom fabricated part used to rigidly connect motor 5208 and 6-port gasvalve 5216.

An electrometer 5210 is shown mounted in a PCI slot mounted to thecomputer motherboard 5221. FID/Electrometer signal cable 5211 andFID/Electrometer reference voltage cable 5212 electrically connectelectrometer 5210 to FID assembly 5202. A 120V AC power inlet 5213 foractuator motor 5208 was added to the PC case by cutting away themounting hole for the bulkhead plug assembly. FID Heater BlockTemperature Control Unit 5213 was added to the PC case by drillingmounting holes for attaching the control unit and allowing the controlknob of the control unit to extend through PC bulkhead wall. OvenCooling Fan/Duct Unit 5215 was added to the PC case to prevent heat fromthe oven and the FID from building up inside the case.

FIG. 53 is another rear view of a computer case 5101 showing analternative set of modifications made to add gas inlets and gas flowcontrol units to the computer case for the pneumatic focusing gaschromatograph of FIG. 52. Bulkhead AC plug assemblies 5302 were added tothe computer case by cutting away mounting holes in the rear exteriorpanel. In this embodiment, oxygen flow control valve 5303 is fluidlyconnected to and between oxygen inlet 5308 and FID assembly 5202 of FIG.52, and is used to control oxygen flow to the FID during operation ofthe FID. Similarly, hydrogen flow control valve 5304 is fluidlyconnected to and between hydrogen inlet 5307 and FID assembly 5202 ofFIG. 52, and is used to control hydrogen flow during operation of theFID. Sample inlet 5305 is fluidly connected to 6-port gas valve 5216 ofFIG. 52.

FIG. 54 shows a side cut-away view of an alternative embodiment of apneumatic focusing gas chromatograph within a modified computer case5601. In this embodiment a piston apparatus is used to pneumaticallyfocus samples instead of a sample loop and a pneumatic focusing gas asin FIG. 52. FID assembly 5402 is added to the computer case by drillingvent holes through the top panel and cutting away bulkhead side wall ofcomputer case 5601 to allow FID assembly 5402 to easily slide into placewhen mounted atop circular oven unit 5404. Column 5403 is fluidlyconnected to and between FID assembly 5402 and piston valve inletassembly 5405. Piston housing 5406 is fluidly connected to piston valveinlet assembly 5405. During operation, piston plunger 5416 is moved bymotor 5408, which is connected to jack screw 5410 through thrust collar5409. Also shown in FIG. 54 are removable media data storage device5407, electrometer 5411, FID/Electrometer signal cable 5412,FID/Electrometer reference voltage cable 5413, non-removable datastorage device 5414, and A/D conversion unit 5415.

FIG. 55 shows a particular embodiment of piston valve inlet assembly5405 of FIG. 54, fluidly connected to piston housing 5416 of FIG. 54.Piston housing 5406 encloses piston 5508, which can move within thepiston housing. Piston 5508 is connected to piston plunger 5416 whichmay be used to move the piston within the housing. Piston housing 5406also includes sample line 5503, which during operation is fluidlyconnected to a pump (not shown) that generates a suction in the sampleline, thereby drawing sample into the piston housing through the pistonvalve inlet assembly 5405. Piston valve inlet assembly 5405 includescheck valve 5504, which allows gas sample flow only in the directionshown by the arrow. Check valve 5504 is fluidly connected to a sampleinlet (not shown). 3-port Tee 5505, is fluidly connected to check valve5504, piston housing 5406, and check valve 5506, which allows gas flowonly in the direction shown by the arrow. 3-port Tee 5507 is fluidlyconnected to check valve 5506. Tee 5507 is also fluidly connected to apneumatic focusing/carrier gas supply. During operation, piston plunger5416 is used to withdraw piston 5508 until the space between the pistonand the piston valve inlet assembly 5405 is fluidly connected to sampleline 5503. The vacuum pump connected to sample line 5503 draws a gassample through check valve 5504 and 3-port Tee 5505, into piston housing5406. At the same time, the pressure of the pneumatic focusing/carriergas flowing through 3port Tee 5507 in the direction shown is greaterthan the pressure in 3-port Tee 5505, causing check valve 5506 to close,thereby preventing flow of the pneumatic focusing/carrier gas intopiston housing 5406. Once the gas sample fills piston housing 5406,piston plunger 5416 is used to drive piston 5508 further into thehousing and past sample line 5503. Once piston 5508 is past sample line5503, the gas sample is no longer entering piston housing 5406. Aspiston 5508 is driven further into housing 5406, the pressure in thehousing increases and closes check valve 5504 which prevents loss ofsample. Piston 5508 is further driven into housing 5406 until thepressure within the housing increases and reaches the pressure in 3-portTee 5507, at which point, check valve 5506 opens and sample enters3-port Tee 5507. Once sample enters 3-port Tee 5507 it is swept into thechromatographic column for analysis. This embodiment may be constructedfrom pre-existing components. For example, any commercially availablecheck valve or solenoid controlled valve that may be opened or closedunder computer control to provide the correct timing may be employed ascheck valves 5504 and 5506. In one embodiment, the check valves areAlltech soft seat checkvalves (part # 02-0129, Alltech, Deerfield,Ill.). The check valves (e.g. solenoid controlled valves) can be mountedin orientations other than vertical if the check valves retain theirfunctionality.

FIG. 56 shows an alternative embodiment of piston valve inlet assembly5405 of FIG. 54, which may be constructed within a stainless steel blockor similar machinable stock. This embodiment includes machined path forgas flow 5602 fluidly connected to inlet port 5603, which receivespressurized carrier gas. Machined path 5602 is also fluidly connected tooutlet port 5608, which is fluidly connected to a chromatographiccolumn. Included within the machinable stock are additional machinedpaths 5609, 5610, 5611 and 5612 which fluidly connect the remainingcomponents of the piston inlet valve assembly 5405. Machined path 5609fluidly connects machined path 5602 to check valve 5604, which may be aball bearing-like sphere in a machined seat that permits gas flow onlyin the direction shown by the arrow. This sphere may be made from anysuitable material, for example, rubber, Teflon, viton, sapphire, delrin,etc. that can withstand the pressures and temperatures to which it isexposed. Machined path 5611 is fluidly connected to machined path 5610,which is fluidly connected to port 5605, which is fluidly connected topiston housing 5406 (not shown). Machined path 5611 is also fluidlyconnected to check valve 5606, which also may be a ball bearing in amachined seat that permits gas flow only in the direction shown by thearrow. If necessary, an o-ring or grommet could be added to the seat toprovide a better seal with the ball bearing. For example, the o-ring maybe fabricated to fit into the interior of the hole and could include alip to prevent it from fully entering the machined path. Sealing wouldoccur with pressure from the ball bearing pressing down on the lip ofthe O-ring/grommet. Such o-rings may be obtained, for example, fromO-rings West (Seattle Wash.). Machined path 5612 fluidly connects checkvalve 5606 to gas sample inlet port 5607. Dead volumes in the assembly5405 may be minimized by the use of appropriate filler poured into thecavities and removed as necessary.

During operation, the piston valve inlet assembly of FIG. 56 functionsin a manner similar to the embodiment shown in FIG. 55. Application of apneumatic focused sample closes check valve 5606 and opens check valve5604, allowing the sample to enter chromatographic column 5603. In someembodiments, dead-volume at 5603 is sufficiently small that backflowwill be negligible. If the dead-volume is too large, a check valve, suchas illustrated at 5604 and 5606, may be installed at the head of column5603 to enable forward carrier gas flow but to block reverse sample flowinto the carrier gas feed line. Any of several commercial check valves(e.g., Alltech soft seat checkvalve, part # 02-0129, Alltech, Deerfield,Ill.) may be used as check valves 5604 and 5606, or such check valvesmay be fabricated. For example, the check valve illustrated in FIG. 58may be used.

Example 20

This example describes an apparatus including a check valve and one ormore crimped flow regulators that may be used for pneumatic focusing ofa sample followed by analysis of the pneumatically focused sample at alower pressure. This method may also be employed with the check valvesto pneumatically focus a sample into a gas chromatograph operating attypical gas chromatographic pressures, for example, at column headpressures of between 10 and 60 psi. In this approach, the high focusingpressure will close suitable check valves, diverting the column flowinto a flow restrictor which will allow on-column focusing of analytes,particularly higher molecular weight analytes (e.g., greater than 16amu), as discussed below. Then, when the high pressure sample has bledthrough the flow restrictor, sample pressure will drop, the check valveswill open (or be opened under computer control), and typical columnpressures will be attained, allowing separation of analytes previouslyadsorbed at the column head.

FIG. 57 shows a schematic diagram of one embodiment of such anapparatus. In FIG. 57, flow control assembly 5701 is fluidly connecteddownstream of column 5603 of FIG. 56, and upstream of FID assembly 5602of FIG. 56. Flow control assembly 5701 includes check valve 5703 andflow regulating device 5705. In this embodiment, check valve 5703 isconfigured to prevent flow at high pressures (e.g. 150 psi and above)from column 5603 to FID assembly 5602, but allow flow at low pressures(for example, below 150 psi, such as below 100 psi, 80 psi, 60 psi ,40psi, or 20psi) from the column to the FID assembly. Flow regulatingdevice 5705 can be a solenoid driven needle valve, a calibrated leak, afrit restrictor, a tapered capillary restrictor, a feedback regulator, amanually operated needle valve, or a crimped capillary flow regulator.Flow regulating device serves to increase the pressure inside the columnand reduce the high flow rate in the direction of the arrow through thecolumn which would otherwise occur upon application of a pneumaticallyfocused sample. As shown in FIG. 57, gas flow through flow regulatingdevice 5705 may be diverted to FID assembly 5602 (dashed line) or may bedirected, for example, to an atmospheric vent or to another detector,for example, a mass spectrometer.

In an alternative embodiment, two flow regulating devices 5705 may beconnected in parallel to the gas line coming from column 5603. In thisembodiment, under high pressure operation, the flow from one of the flowregulating devices is directed to FID assembly 5602 (for example, asshown by the dashed line in FIG. 57), and the flow from the other flowregulating device is directed to a second detector, for example, a massspectrometer. By adjusting the relative flow rate of the two flowregulating devices, sample emerging from the chromatographic column maybe apportioned to the two detectors as appropriate. For example, if thesecond detector is a mass spectrometer, the flow directed to the massspectrometer will be adjusted to a lower level than the flow directed toFID assembly 5602 to maintain the low pressure needed for operation of amass spectrometer.

In yet another embodiment, one (or more) additional measurement devicemay be connected through suitable flow regulating devices to the sampleline between 5703 and 5602. This additional device (for instance a massspectrometer, could sample a suitable proportion of the flow leaving thechromatographic column under the low pressure conditions which applyafter the pneumatically focused sample pressure drop has occurred andflow through flow restrictor 5705 has been transferred to check valve5703. In this embodiment, the main flow passes through valve 5703 to FID5602 while a suitably regulated flow is directed through the flowregulating device (not shown) to a second detector, for example, a massspectrometer. By adjusting the relative flow rate of this flowregulating device, sample emerging from the chromatographic columnoperating under low pressure conditions may be apportioned to the twodetectors as appropriate. For example, if the second detector is a massspectrometer, the flow directed to the mass spectrometer will beadjusted to a lower level than the flow directed to FID assembly 5602 tomaintain the low pressure needed for operation of a mass spectrometer.

During operation of flow control assembly 5701, a pneumatically focusedsample is introduced to column 5603. Pneumatic focusing of the sampleinvolves increasing the pressure applied to the sample as it isintroduced to the column. At the time the pneumatically focused sampleis introduced, operational column pressure may be any pressure, forexample, a low pressure (e.g., 10-60 psi), an intermediate pressure(e.g., 60-120 psi), a high pressure (e.g. 120-1200 psi) or an extremelyhigh pressure (e.g. greater than 1200 psi). Regardless, application ofincreased column pressure of the pneumatically focused sample will closecheck valve 5703 when the sample pressure rises above the columnpressure. This will divert flow of the pneumatically focused samplethrough flow restrictor 5705. This flow is desirably at a ratesufficiently low to concentrate analytes, particularly higher-weightanalytes (e.g., greater than 16 amu), at the head of the column. Whenthe pneumatically focused sample is exhausted, that is, most of thesample volume has passed through flow restrictor 5705, column pressurewill drop, check valve 5703 will open, and carrier gas flow through thesystem will resume. Then, for example, when the column temperature isincreased, such as by temperature programing, separation of the analytesadsorbed at the head of the column will occur.

At the pressures used for pneumatic focusing, check valve 5703 will beclosed, preventing direct flow to FID assembly 5602. Instead, flow isdirected to flow regulating device 5705, which is functioning as aninline pressure increasing/flow decreasing valve. For example, flowregulating device 5705, by restricting flow, maintains the pneumaticfocusing pressure that is applied to the sample by either a pneumaticfocusing gas or a piston device. Once the sample is introduced to column5603 it may be desirable to lower the pressure to aid in chromatographicseparation of sample components, to reduce consumption of the carriergas associated with high pressure flow, or to reach a flow more suitablefor a mass spectrometer. Once the pressure is lowered, check valve 5703will open, permitting direct flow of sample components from the columninto FID assembly 5602 or other associated detectors such as describedin the previous paragraph.

When a sample contained in a sample loop is pneumatically focused by ahigh pressure gas, and then introduced into a chromatographic column,high pressure gas remains in the sample loop. The high pressure gas mustthen be vented to allow additional sample to enter the sample loop.Venting may be accomplished by allowing gas to escape from one end ofthe sample loop. However, in some applications it may be undesirable tolet the high pressure gas enter the sample pump or the sample line. Gasflow into the sample pump or sample line may be prevented by a checkvalve. A second check valve that permits venting to atmosphere also maybe employed.

FIG. 58 is a diagram showing a particular embodiment of a check valvethat can be used, for example, in pneumatic focusing gas analysissystems such as the apparatus of FIG. 57, or the apparatus of FIG. 55.For example, the check valve may be used to prevent backflow of highpressure gas into a sample line or sample pump. Check valve 5801includes Swagelock tube fittings 5802, spring 5803, ball bearing 5804,outer Teflon tubing 5805 and inner Teflon tubing 5806. Outer Teflontubing 5805 is connected to the two Swagelock tube fittings 5802 at bothends. Inside of outer Teflon tubing 5805 is fitted inner Teflon tubing5806. The outer diameter of inner Teflon tubing 5805 is such that itfits tightly within the outer Teflon tubing 5805 and prevents gas flowbetween the outer surface of the inner tubing and the inner surface ofthe outer tubing. Ball bearing 5804 is of a diameter that is larger thanthe inner diameter of inner Teflon tubing 5805. Spring 5803 preventsball bearing 5804 from forming a seal against the Swagelock tube fitting5802 shown at right in FIG. 58, but ball bearing 5804 may form a sealwhen it is pressed against the end of inner Teflon tubing 5805 at left.Thus, in operation, gas flow is permitted from left to right in FIG. 58.

It should be recognized that particular check valves are not needed toestablish the functionality of the apparatus shown in FIG. 57. Rather,any gas valve (commercial or fabricated) can function to regulate flowduring pneumatic focusing of analytes at the column head. As will beappreciated by one of ordinary skill in the art, the molecular weightsof compounds that are concentrated at the head of the column duringpneumatic focusing will depend, for example, on the column type, thestationary phase and the temperature.

FIG. 59 shows a particular flow regulating device that may be used inpneumatic focusing apparatuses such as those shown in the systems ofFIG. 1 and FIG. 57. Crimped flow regulating device 5901 includes twoSwagelok tube fittings 5902, which are disposed at either end of metaltubing 5903, which may, for example, be copper tubing or steel tubing.In operation, the flow rate through crimped flow regulating device 5901is adjusted by the following method.

1. Metal tubing 5903 is crushed in a first direction, such as in a viceor a press, so that no flow is observed (or possible) through crimpedflow regulating device 5901 at the desired pressure (e.g. the pneumaticfocusing pressure desired). Flow through crimped flow regulating device5901 may be monitored by connecting one end of the device to a supply ofgas at the desired pressure, and connecting the other end to a flowmeter, such as a soap bubble flow meter known in the art.

2. While observing the flow meter, tubing 5903 is crushed in a seconddirection, such as a direction substantially perpendicular to the firstdirection, until flow through device 5901 is observed. Crushing in thesecond direction is conveniently done using a pair of pliers. As thetubing is crushed in the second direction, the flow will increase, andcrushing is ceased once the desired flow rate at the desired pressure isobserved. In practice, there is some elasticity of the tubing, and theflow rate should be monitored for a period after crushing in the seconddirection that is sufficient for the flow rate to stabilize. If thedesired flow rate is exceeded, the process may be repeated.

An advantage of a crimped flow regulating device is its relativetemperature insensitivity. Thus, the flow regulating device may beplaced inside of a pneumatic focusing instrument, such as between aheated column oven and a heated FID. In contrast, commercially availableneedle type valves used for flow regulation, such as the PNEUMADYNEvalve described above, are temperature sensitive in that they showunacceptable variation in flow rate with temperature and typicallyinclude components that are not resistant to temperatures as high as maybe desired for a column oven or an FID.

With reference to FIG. 52, when a separated sample is transporteddirectly from a metal chromatographic column such as 5203 to a detectorsuch as FID 5202, the crimping procedure may be applied directly to theend portion of the column itself. Crimping the column itself eliminatesthe need for flow regulating device 5901 by accomplishing its functiondirectly. If so crimped, the column should not contain packing materialin the portion to be crimped. That is, a substantial end portion ofcolumn should remain unpacked. Thus it would be possible to cut andremove an unusable end portion of the column and still have additionalunpacked column for remaking the crimp. In addition to simplifying theoverall design, direct column crimping provides for a more leak-freesystem, as potential leaks at the high pressure, upstream end of flowregulating device are circumvented.

Example 21

This example describes additional embodiments of analyticalinstrumentation contained within a personal computer case. Inparticular, this example concerns the construction of a massspectrometer based upon a commercial residual gas analyzer (RGA) withina commercial personal computer case. The computer would also containtypical computer components such as a processor, RAM, hard drive, etc.,which would be used to control and pass data to and from theincorporated RGA. This example is based upon the commercial RGA offeredfor sale by Extorr (New Kensington, Pa.) having the dimensions3.3″×4.8″×7.5″. This small quadrupole mass spectrometer is provided witha negative pressure (relative to atmospheric pressure) to allow itsoperation. In this example, the negative pressure is provided in achamber, the chamber also provided within a commercial personal computercase. Furthermore, a source of sample, such as a gas chromatograph, forexample, a pneumatic focusing gas chromatograph is also provided withinthe personal computer case.

A suitable negative pressure is provided using any standard set ofcomponents as would be familiar to someone skilled in the art. Suchcomponents include, but are not limited to, a hermetically sealed metalcontainer coupled to the vacuum connection of the commercial RGA.Provision for vacuum pumping of the vacuum chamber by, for instance, aturbomolecular pump, is supplied by suitable and standard vacuumfittings welded or otherwise affixed to the metal vacuum chamber.Provision for sample introduction from either an external sample source,or from the effluent of a chromatographic column, such as a gaschromatographic column is provided as well.

Pumping for the RGA and associated vacuum housing is provided, forexample, by a vacuum pump such as a turbomolecular pump. Any such pumpmay be employed, with small pumps which would easily fit within thecommercial computer case being advantageous, leaving more room for othersystem components. A particularly suitable pump has been described byNASA. This particular pump has approximately cubic dimensions of 2.25inches. Such a device easily fits inside the commercial computer caseand be coupled to the Extorr RGA, also within the case. As described inthe NASA brief, this miniature turbomolecular pump could be combinedwith a miniature diaphragm fore pump which would also fit within thepersonal computer case.

The NASA-described turbomolecular pump is proposed rather than extant,but shows the miniaturization possible within the current massspectrometric/pumping art. Slightly larger turbomolecular pumps are nowavailable. For example, the turbomolecular pump may be an ATH 31 pump byAlcatel (Hingham, Mass.) which fits within a 4″ cubed space.

Example 22

This example describes a system and method for detecting particulatematter in a gas sample. More particularly, this example describes amethod for visualizing and counting the number of spores, such as moldand bacterial spores, in an air sample.

Aerosols may be defined as solid or liquid particles suspended in air.As such they can encompass such terms as aerosol particles, particles,particulate matter, dust, haze, smoke, etc. Particles are naturallypresent in outdoor air and are also introduced into outdoor or indoorair by human activities. Inhalation of certain types and sizes ofparticles can be hazardous to health. Atmospheric particles range insize from millimeter to nanometer sizes. Larger particles soon fall toearth unless maintained airborne by high wind turbulence. Smallerparticles may remain airborne indefinitely. Details of atmosphericparticle sizes, formation and loss, and human health implications aredescribed in such texts as Smoke, Dust and Haze by Sheldon Friedlander.

In typical ‘integrating’ particle detectors such as nephelometers andcondensation nuclei counters, a number of particles collectively absorbor scatter measurable amounts of light. Such instruments are neithersensitive to individual aerosol particles nor to low numbers of aerosolparticles. Although optical particle counters can detect and ‘size’individual aerosol particles, such instruments are expensive andcomplex. In contrast, the disclosed methods and systems are simple andinexpensive, capable of detecting very low numbers of particles (such as1 particle per cubic centimeter) and capable of operating for very longperiods completely unattended.

When air is compressed rapidly, adiabatic heating occurs. Such heatingmore than compensates for the increase in water vapor concentrationassociated with the volume reduction. Adiabatic heating prevents watercondensation. However, subsequent to the compression step, heat will belost to the surroundings, cooling will occur, and water may condense inthe system. This effect has been used herein to selectively condensesuch water on certain types of aerosol particles.

When water vapor saturations greater than 100% occur, water vapor isinclined to condense to the liquid phase. Due to the Kelvin Effect (seeSmoke, Dust & Haze, Sheldon Friedlander), such water will tend tocondense on preexisting surfaces rather than homogeneously form newwater vapor droplets. This is the phenomenon involved in so-called“cloud-seeding.” According to the Kelvin Effect, larger aerosols will bemore favored thermodynamically to condense water vapor and at lowersupersaturation. This effect is described by a simple mathematicalequation, the Kelvin Equation. However, one term in this equation, thesurface tension of the resultant liquid droplet, is difficult orimpossible to predict for the wide range of aerosol particles present inthe atmosphere. Expressed another way, the physical nature of theaerosol that can potentially serve as a condensation nucleus is animportant parameter in determining whether that aerosol particle willcondense water vapor at any given supersaturation. In general, sucheffects must be determined experimentally rather than theoretically.

A system for the controlled pressurization or depressurization of an airsample at a controlled rate is provided. In the case of pressurization,the rate of pressurization will determine the development of controlledsupersaturation with the ability to condense water vapor selectively onparticles. This controlled pressurization may be obtained either bycompressing at a slow rate, or by compressing at a faster rate, and thenstopping the pressurization step and waiting for cooling andcondensation. In the case of depressurization, since adiabatic coolingenhances water condensation, the method consists of slowly expanding thevolume containing the air sample. In either situation the air sample maybe contained in a small piston-containing chamber to which it isintroduced before the measurement begins.

Particles are drawn with the associated air sample into a cellconstructed for that purpose. Details of the cell are given in theexamples below. The cell is connected to a piston device for drawing theair sample into the cell by piston expansion. Following influx of theair sample, a valve is closed and the piston is compressed to thedesired pressure to initiate hydration of the particles. No specialcoating on the inside of the cell and piston has been found necessary,but may be used in some embodiments. If desired, the inside of theapparatus may be coated with Teflon or some other hydrophobic coatingwhich prevents water condensation of the surface of the piston and cellitself. Particles may visualized by the light beam from an inexpensivelaser pointer which enters and exits the cell through windows placedopposite each other for that purpose. Particles may be detected by awebcam whose viewing axis is 90 degrees from the light beam propagationline, also through a window provided for that purpose. Concurrently,additional light sensors could be present in the cell. Such sensorscould be constructed, for instance, from the receiving end of an opticalfiber connected to a computer spectrometer. Alternately, they could beany of a number of light sensing diodes or other devices. Theseadditional light sensors could provide measurements of light scatteringor attenuation as in a condensation nuclei counter or an integratingnephelometer. In this case they could be provided either along the lineof propagation of the light source or at angles, such as right angles,to measure, respectively, transmission and/or scattering of thepropagated light beam.

The examples described below involve controlled pressurization of airsamples containing ‘normal’ room air, or room air to which spores havebeen intentionally added. Additionally, such air samples could besubjected to depressurization or expansion by withdrawing the piston.Under these controlled conditions, selective hydration of certain typesof aerosols such as spores may be accomplished.

In some embodiments, the methods include recording of individualparticles grown up by water condensation to a size viewable by a webcam.A computer continuously records a bitmap (or other format) image fromthe camera and software parses the individual bits of the image for thepresence of a strong light signal. Typical webcams record images at 30Hz, or 30 frames per second. Such rates are suitable for this method.For this method to work, it is not necessary to magnify an individualparticle to a size where it would occupy more than 1 bit in the image.Rather, a single bit records the presence of a light scattering aerosolparticle actually much smaller than the area visualized by the bititself. However, spores and other aerosol particles upon whichcondensation has not occurred are too small to produce significantscattering to be recorded with the web cam. Thus, in the absence of thewater condensation step, spores or similar particles produce no signal,i.e. the bitmap is ‘empty’ or all black. The number of particles in thefield of view of the camera/beam system is easily determined fromgeometrical and optical considerations. Viewed volumes on the order of acubic centimeter have been typically viewed in prototype instruments andone or more particles are routinely visualized after water condensation.Thus, the prototype instruments have a ‘nominal’ detection limit of ˜1spore per cubic centimeter, although much higher numbers of spores percubic centimeter may be detected. An upper limit may occur whenindividual spores overlap in the bitmap image. Under many circumstances,however, if the spore count were this high, there would be no need tomeasure it accurately. However, if there was need to measure sporeconcentration accurately, the air sample could be diluted, for example,quantitatively, with filtered air before it enters the visualizationcell.

The disclosed methods and systems are described further in the followingexamples. These examples are provided for illustrative purposes and arenot meant to limit the invention in any way.

1. Particulate Detection System

FIG. 60 is a schematic of a working embodiment of a system useful formeasuring the number and size of particulates, including spores, for anygiven gas sample, including air. The following components, as well astheir connections, will be discussed with reference to FIG. 60. A moredetailed explanation of certain components is also included.

FIG. 60 illustrates the aerosol detection system 6013. A workingembodiment of system 6013 has been used to nucleate spores of mold grownin a 1-pint jar on a carbohydrate medium in room air. The system 6013pressurizes air in the cylinder 6003, after which the pressurized aircools with heat lost to the surroundings. Upon compression, room airundergoes adiabatic heating. The air inside cylinder 6003 then goesthrough a period of controlled cooling and heterogeneous nucleation,wherein water vapor condenses on aerosol particles in the air. Laserpointer 6005 is used to illuminate the particles once they havenucleated, and web cam 6007 is used to record a bitmap (or equivalent)image the nucleated particles as they are illuminated. The web cam isinterfaced with desktop computer 6002, and the movies can be viewed frommonitor 1, using, for example, the INTEL Auto Snapshot program. Valve6008 is used to release the pressurized air, and draw in new samples.

Cylinder 6003 is pressurized by means of trailer jack 6004; cylinder6003 is fastened to trailer jack 6004 by u-clamp 6006.

Relay box 6012 is interfaced with trailer jack 6004 to allow remotecontrol of trailer jack 6004, by means of the relay box 6012. Relay box6012 is also interfaced with the computer 6002, by means of parallelport cable 6014. The interface allows trailer jack 6004 to be controlledremotely by computer 6002, for example, with the use of the TEKBASICprogramming language. Relay box 6012 is connected to trailer jack 6004by means of power cable 6017. Relay box 6012 is also connected to Variac6015, by means of power cord 6016. Variac 6015 is then plugged into thewall outlet 6018. The Variac 6015 regulates the voltage down to 12V.Relay box 6012 is then powered at 12V from the Variac 6015.

The system also includes components that may be used to cool thecompression cylinder 6003. Water at a temperature lower than thecylinder may be flowed through tubing 6010, from water source 6011.Water travels through tubing 6010 into copper coil 6009 which surroundscylinder 6003. Water then continues through tubing 6010, and is disposedfor example in a drain or sink.

In an alternative embodiment, the system components described above areall contained within the case of computer 6002.

Expanded views of different portions of FIG. 60 are shown in FIGS. 61and 62. These FIGS. refer to the description just given and aredescribed further below.

FIG. 61 is an illustration of the end of cylinder 6003 in FIG. 1 andcomponents attached thereto. All the following components, as well astheir connections, will be discussed with reference to FIG. 61.

When air is compressed in cylinder 6103, and particle nucleation hasbegun to occur, the particles are illuminated by means of the laserpointer 6105, which is attached to cylinder 6103 by interface 6106. Theilluminated particles are then filmed and documented by the web cam6101, which is attached to cylinder 6103 through interface 6102 and isin electrical connection with the desktop computer 6108. The nucleationof particles inside cylinder 6103 can then be viewed on desktop computer6108 by using the INTEL Auto Snapshot program. Air samples in thecylinder are exchanged by the use of the screw valve 6103. An optionalfilter 6104 can be attached to screw valve 6103 in order to filter outany larger aerosol particles. In a working embodiment, all of theaforementioned components that are connected to the cylinder 6103 wereattached by drilling into the side of the cylinder 6103, then tappingthe holes for ¼ inch pipe fittings.

FIG. 62 is an illustration of interface 6102 in FIG. 61, which is usedto fasten the web cam 6101 to cylinder 6103. All of the followingcomponents, as well as their connections will be discussed withreference to FIG. 62. In FIG. 62, webcam 6201 is attached with fitting6202 to housing 6205 held together by bolts 6203 and connecting plates6204.

2. Operation of the System

Experimental images and graphs obtained using the system described inFIGS. 60-62 are shown FIG. 63. FIG. 63 depicts three differentexperiments. Each experiment is depicted by a chart (charts 1-3) as wellas two sets of web cam images for each experiment. Each set of threeimages stacked vertically refers to each of 3 exemplary experiments. Thebottom set of 3 web cam images are shown as recorded by the webcam.These images have a black background with blotchy areas where the laserbeam reflects off the cell walls. These reflections have nothing to dowith aerosol particles and can be eliminated through further celldesign. In addition, each webcam image shows a number of individualparticles. Image 1 shows a single particle indicated by an arrow. Images2 and 3 show a plurality of particles, only a few of which are indicatedby arrows. The middle set of photos are color reversals of the bottomset. These are included only for clarity in that the lower, black setmay not reproduce well. These middle images present the same informationas the lower set.

Chart 1, Chart 2, and Chart 3 illustrated in FIG. 63 are graphical andbitmap representations of data collected using the system 13.

Referring back to FIG. 60, when the trailer jack 6004 compresses thecylinder 6003 in the system 6013, and a subsequent waiting period forcooling is employed, the gas inside the cylinder goes through a periodof heterogeneous nucleation. The waiting period typically comprisesanywhere from 10 seconds to several minutes.

An exemplary procedure follows:

-   -   1) Cylinder 6003 is compressed to a certain compression ratio        during which time the gas heats substantially adiabatically.        This compression pressure is indicated in the charts in units of        10 psi above atmospheric pressure which is approximately 15 psi.    -   2) The relative humidity inside said cylinder 6003 initially        decreases due to this heating process. This heating has a        stronger effect than the volume compression on the relative        humidity.    -   3) Heat is lost to the cooler surroundings, which causes the        compressed gas to cool. When, due to this cooling, the sample        relative humidity increases to a particular value that is higher        than one hundred percent, the moisture in the gas begins to        condense on selected aerosol particles that may be in the        sample. Depending upon the size and character and type of        aerosol particles, water will condense on those particles at a        characteristic pressure, time, temperature or relative humidity        following compression.

While cylinder 6003 is in the process of being compressed adiabatically,the moisture will not condense on the particles due to the fact that theheat created by the increasing pressure will cause the vapor pressure ofthe water to rise fast enough so that no water is allowed to condense onthe particles in the sample. When the sample inside cylinder 3 iscompressed and then allowed to cool for a short period of time, heat islost from the sample to the walls of cylinder 6003. When enough heat islost from the gas, the vapor pressure of the water lowers to a pointwhere it will begin to condense on some of the aerosol particles in thegas. The condensation that occurs in the sample tends to happen to thelargest and/or most hygroscopic particles first. As sample temperaturedrops, and in turn the relative humidity increases, the more hydrophilicand/or larger particles nucleate and are visualized first. So bycompressing the cylinder 6003 to varying pressures it is possible tocause the water in the air sample to condense on different types ofparticles in the sample.

The disclosed embodiment of the spore detector included a trailer jackthat had only a single compression speed. Hence, the procedure ofcompression, followed by waiting for cooling and condensation, wasemployed. A more general approach is to use a variable speed motor toenable compression at any desired rate. At sufficiently low compressionrates, heat loss to the surroundings will occur substantially ascompression heating occurs. In this mode, no waiting period for coolingand condensation is needed; rather, condensation on particles occurs ata particular pressure or compression ration without any waiting period.Such a compression mode is isothermal in nature rather than adiabatic innature. In the “isothermal” mode, the presence of spores would bedetected by their hydration at a lower compression ratio relative toother, non-spore aerosol particles in a gas sample, such as an airsample.

Referring still to FIG. 60, it is possible to inject a sample of normalroom air that has been contaminated with spores into cylinder 6003 usingthe valve 6008, and compress the sample to a point where the spores willbegin to nucleate. The pressure required to nucleate and visualize theseparticles in the laser beam has been shown to be significantly lowerthan the pressure that is required to allow the ambient particles in anormal sample of room air to nucleate. This means that it is possible toidentify the presence of spores in a sample of room air.

Chart 1 of FIG. 63 is a representation of an experiment in whichordinary room air was injected into cylinder 6003 using valve 6008 ofFIG. 60. The sample was then compressed in cylinder 6003 using trailerjack 6004, in increments of 10 PSI. Chart 1 shows that there areliterally no spores seen nucleating at any of the lower pressureintervals. Then, at roughly 50 PSI above normal atmospheric pressure,the production of nucleated aerosol particles jumps up rapidly. This isbecause in this sample of normal room air no ambient particles existthat are large enough, or hygroscopic enough, to nucleate at pressureslower than 50 PSI above atmospheric pressure. After the sample reachespressures higher than 50 PSI above atmospheric pressure, and the cell isallowed to cool, the relative humidity rises to a point high enough thatwater will begin to condense on the ambient particles in the air.

Chart 2 of FIG. 63 is a representation of another experiment in whichspores were hydrated and visualized at pressures lower than thoserequired to hydrate aerosols present in the same room air.

Spores were prepared for this experiment by storing a piece of bread,about 2 cm×2 cm, in a glass container for a period of several weeks.During this time, mold grew on the bread and eventually formed spores.These spores were suspended by shaking the jar. Air from the jar wasdrawn into the visualization chamber by the piston through a tubeprovided for that purpose. This tube connected the spore jar fluidlywith the compression chamber. Air withdrawn from the mold chamber wasreplaced through another inlet to the mold chamber. This replacement airoriginated from the room. Air originating from the room could either betaken directly, in which case it contained ambient aerosols; or it couldbe filtered before entering the mold growth chamber, thereby removingthe larger room aerosol particles. In this spore experiment, it was notdetermined whether the spores existed individually as supendedaerosols,or whether they were present as agglomerates of multiple spores. Innormal spore release by, for example, molds, individual spores arereleased. However, in terrorist application of virulent spores, it isoften difficult to disperse individual spores, and less effectiveagglomerates of spores are released. It may be possible to differentiatesingle spores and agglomerated spores on the basis of their relativehydration pressures.

In this experiment room air that had been contaminated with spores wasinjected into cylinder 6003 using valve 6008 of FIG. 60. The sample wasthen compressed in cylinder 6003 using trailer jack 6004, in incrementsof 10 PSI. Chart 2 indicates that numerous particles are nucleating atpressures as low as 20 PSI above atmospheric pressure. At 20 PSI aboveatmospheric pressure, Chart 1 shows that no particles were seennucleating when room air with no added spores constituted the sample.The experiment that produced Chart 1 was identical to the experimentthat produced Chart 2, except that there were no spores added to the airsample used in the experiment for Chart 1. So, the only particles thatcould have been nucleating at pressures as low as 20 PSI aboveatmospheric pressure were the foreign spores that were contaminating theair sample that was used in the experiment for Chart 2. Thisdemonstrates that it is possible to identify spores in a gas samplethrough the use of the system 6013 of FIG. 60.

Chart 3 of FIG. 63 is a representation of a third experiment. Thisexperiment was run in a manner identical to the experiment that producedChart 2. The data in Chart 3 shows results that are consistent withthose found in Chart 2, and shows that the data in Chart 2 isreproducible. This means that the conclusions drawn from Chart 2 can bedrawn from another, identical experiment that was performed at adifferent time than the experiment that produced Chart 2.

In addition to simply identifying the presence of foreign particles in asample of gas, it is possible to count the particles in the photo anduse an equation to give an estimate of particles per cubic cm in theoriginal air sample. The equation describes the volume of compressed airin which the spores are counted. The compressed air sample illuminatedby the laser pointer has a volume of pi*r^2*1. Here, r is the laser beamradius, 1 is the length of the laser beam that falls within the field ofview of the web camera. The values of r and 1 may be measured with amillimeter scale by directing the laser pointer beam onto the scale, andby viewing the scale at the appropriate distance with the web cam. Thiscalculation provides the volume in which the spores were detected. Sincethe air during detection has been compressed, correction for thiscompression step will give the original number of spore particles perunit volume. This calculation, for example, would then beN=pi*r^2*1*P/atm psi. The quantities r and 1 are defined previously. Pis the pressure to which the cell was pressurized and atm is atmosphericpressure in the same units. Alternatively, P/atm is the isothermalcompression ratio utilized for a particular hydration event.

In addition to counting the number of aerosol particles per unit volumeit is possible to estimate their size with use of the equation,D=2((0.0525343*P)/(N*T)). In the equation, D represents the diameter ofthe individual particles being nucleated. N represents number ofparticles being seen hydrated at any point in time. P represents thepressure of the gas at the time when you are trying to determine thesize of the particles. T represents the absolute temperature of the gas.By taking a picture of the nucleating particles as captured by the webcam 21 it was possible to determine the approximate size of theparticles being seen in the picture.

A program for counting the number of particles in a picture has beendeveloped using the MATLAB programming language which offers imageprocessing software. With this program, it is possible to find thenumber of particles that are hydrating in the cylinder 6003 of FIG. 60at any point in time. This is done by parsing the individual bits of thewebcam bitmap image and looking for high light intensities. Then, giventhe pressure and temperature in said cylinder 6003, it is possible todetermine the average size for the particles hydrating.

The aforementioned experiments describe pressurization of a room airsample to varying pressures above atmospheric pressure followed by adelay waiting time for cooling and condensation to occur. This waitingtime typically represents a few seconds to a few minutes.

Alternatively, the methods may be practiced by slow expansion of thepiston in a chamber into which room air has been introduced. In thiscase, condensation may occur without a waiting period, since adiabaticcooling should immediately produce an increase in relative humidity bydecreasing the water vapor pressure. The principal variable in thissystem will simply be the rate of piston expansion. Thus, a pistonchamber in which the piston movement rate can be controlled is required,for example by use of a variable voltage dc motor. These experimentsmay, for example, be conducted as follows:

-   -   1) The piston is compressed to its minimum distance to expel        most of the air from the previous sample.    -   2) The piston is drawn back a predetermined distance, such as ½        way between its fully compressed and fully expanded positions.        During this expansion air from the sample enters the chamber.    -   3) The valve connecting the piston to the atmospheric or other        sample is then closed and the air sample is allowed to reach        room temperature.    -   4) The web camera is initiated, obtaining images of the cell        contents every {fraction (1/30)} second.    -   5) The piston is then slowly further withdrawn towards full        expansion.

Adiabatic cooling produces condensation upon selected preexistingparticles. The camera then records the condensation of water vapor ontopreexisting aerosol particles or spores. With a record of pistonposition and/or cell pressure and/or temperature, the point at whichvarious types of aerosol particles or spores hydrate may be determined,and used to determine whether spores can be distinguished from ‘normal’room aerosols. Furthermore, different types of spores/particles may bedistinguished by the recorded piston position, cell pressure and/ortemperature at which they hydrate.

-   -   6) In an alternative approach, following step 4), the piston is        slowly compressed rather than withdrawn. If such compression is        done slowly, the compression may proceed substantially        isothermally, rather than (semi) adiabatically, and hydration of        spores will occur at a characteristic isothermal compression        ratio.

Either 5) or 6) may be employed successively in a particular sporedetection experiment. That is, one air sample may be subjected to steps1-5, and the next subjected to steps 1-4, then 6.

3. Webcam Detection of the Hydration Process

FIGS. 64 and 65 depict a series of webcam photos taken during thehydration of spores from moldy bread at 40 psi. This is a differentexperiment from the experiments shown in FIG. 63. FIG. 64 shows asequence of frames taken at 30 Hz, the base frequency of the webcam.Each frame is taken {fraction (1/30)} of a second after the previousframe and after the onset of hydration after the cell was pressurized to40 psi. FIG. 65 shows a longer sequence of the same experiment, thistime showing only every 10^(th) frame so that ⅓ second elapses betweenframes. The direction of laser beam propagation is illustrated in thefirst frame of each sequence. A few frames are individually numbered toillustrate the sequence.

4. Continuous Monitoring to Detect Sudden or Occasional Exposure toExtraneous Spore Aerosol Particles

This example describes a method of continuous monitoring for thepresence of extraneous spores which could potentially be harmful tohealth. The apparatus described in this section is operated continuouslyby a personal computer using the methods described above. A humanindividual may be automatically notified by said computer if an unusualparticle situation occurs.

Compression of an air sample produces adiabatic heating that raises thevapor pressure of water vapor present in the air sample. In spite of thevolume decrease associated with compression, water will not condenseunder adiabatic conditions. However, if the sample is allowed to cool ata controlled rate during the compression step it is possible to regulatethe sample relative humidity so that a well-controlledtime/temperature/relative humidity profile occurs. Thus, particles inthe air sample will be exposed to gradually increasing relativehumidity. In principle, for particles of a homogenous chemicalcomposition, the largest particles should hydrate first, followedsuccessively by increasingly smaller particles. This phenomenon can befollowed by the laser illumination, webcam recording described above.Alternatively, this phenomenon can be followed by monitoring the lightscattering particles with a standard, low-tech photometer as used in acondensation nuclei counter. An inexpensive laser-pointer type lightsource may be employed in either case. Thus a particular intensity/timecurve would represent a particular size distribution for asize-polydisperse, chemically-homogeneous aerosol. The details of thiscurve would depend upon the hygroscopic properties of the original“seed” aerosol. This combination of size distribution and hydroscopicityfor a size-polydisperse aerosol could easily be measured for a givenchemically-homogeneous aerosol. If components of the original aerosolparticle are water soluble they would dissolve during thishydration/growth period. If the aerosol particle is not soluble per se,as is the case with a bacterial spore, then the particle size andsurface free energy of the particle would determine its particulartemporal light scattering curve.

Another approach is to use slow, gradual expansion of the original airsample within the piston chamber with concurrent measurement of eitherparticle number via web cam and/or total light scattering via aphotometer. This expansion would be carried out either by drawing afresh air sample through the chamber with an auxiliary pump, followed bygradual expansion, or by drawing a new air sample into the chamber bypartial expansion of the piston, following by closure of the valve toprevent more incoming air, followed by subsequent expansion of thepiston. This expansion would be neither adiabatic or isothermal, butin-between these limiting cases, with the extent of cooling dependentupon the expansion rate and the rate of heat transfer to thesurroundings.

In the open atmosphere there will be a mix of particle sizes andparticle chemical composition that would produce a varyingtime/hydration/light scattering curve. Gradual compression or expansionof an air sample would record a light intensity hydration curve whichcould be stored and then compared by pattern- or source-recognitionsoftware to previous history to look for something quantitatively out ofthe ordinary. The system could be extensively tested on both ambientaerosols and upon selected nonvirulent spores which will serve asanthrax or other virulent spore surrogates.

Once an automated compression/light scattering system as described abovewas operational, it would continuously and repeatedly record connecteddata records of light scattering and/or number of condensation nuclei.This data would form a continuous record which could then be compared inreal time with each new data file using pattern or source recognitionsoftware. In this way any unusual circumstance would be immediatelyrecognized.

Certain preferred embodiments are described herein. Persons of ordinaryskill in the art will realize that the scope of the present inventioncan vary from the particular embodiments described herein. The truescope of the present invention should be determined by reference to theattached claims.

1. A gas chromatograph and gaseous sample analysis system, comprising: asample loop for receiving a gaseous sample; a separatory column fluidlyconnected to and downstream of the sample loop; an inlinepressure-increasing device which is located downstream of the separatorycolumn and which is configured to increase system pressure to at least150 psi to pneumatically focus the gaseous sample; and a detectordownstream or upstream of the pressure increasing device for detectinganalytes.
 2. The system of claim 1 where the inline pressure-increasingdevice is further configured to reduce linear flow rate to lower thanlinear flow rate through the system prior to increasing the pressurewith the inline device.
 3. The system of claim 1 where the inlinepressure-increasing device is further configured to increase linear flowrate to higher than linear flow rate through the system prior toincreasing the pressure with the inline device.
 4. The system of claim 1where the inline pressure-increasing device is further configured tomaintain linear flow rate substantially the same as linear flow ratethrough the system prior to increasing the pressure with the inlinedevice.
 5. The system of claim 1 where the sample loop is of sufficientcapacity to provide adequate analyte sensitivity once the sample ispneumatically focused, and wherein the system is further configured toinject all of or a portion of the pneumatically focused sample into theseparatory column.
 6. The system of claim 1 including plural separatorycolumns.
 7. The system of claim 1 including plural detectors.
 8. Thesystem of claim 1 and including a vacuum pump to draw a gas samplethrough the column.
 9. The system of claim 1 and further comprisingplural separatory columns.
 10. The system of claim 1 and furthercomprising plural sample collection coils and plural separatory columns.11. The system of claim 1 and further including a sample collection pumpfor drawing the gaseous sample into the gas sample loop.
 12. The systemof claim 1 and further including a computer for controlling the system.13. The system of claim 12 where the computer is operated by a neuralnetwork and expert systems.
 14. The system of claim 1 where the gaschromatograph is located on a microchip.
 15. The system of claim 12,wherein the system is contained within a computer case.
 16. The systemof claim 1, wherein the inline pressure increasing device is selectedfrom the group consisting of a calibrated leak, a frit restrictor, atapered capillary restrictor, a feedback regulator, a needle valve, anda crimped capillary flow regulator.
 17. The system of claim 15, whereinthe computer case is selected from the group consisting of AT, BATX,ATX, MATX, LPX and microATX compatible cases.
 18. The system of claim15, wherein the computer case is selected from the group consisting offull tower, tower, mid-tower, microtower, desktop, rackmount and serverchassis cases.
 19. The system of claim 1 where the sample loop isconfigured to withstand system pressure used to pneumatically focus thesample.
 20. The system of claim 19 where the sample loop is configuredto withstand pressures from 200 psi to 2,000 psi.
 21. The system ofclaim 1 where the inline pressure-increasing device is configured toincrease system pressure to a pressure of 150 psi to 15,000 psi.
 22. Thesystem of claim 1 where the inline-pressure-increasing device isconfigured to increase system pressure to a pressure of 200 psi to 2,000psi.
 23. The system of claim 1 further including a valve configured todirect a carrier gas through the sample loop containing the first volumeof the gaseous sample as the inline pressure-increasing device increasessystem pressure.
 24. The system of claim 1 where the inline-pressureincreasing device is further configured to decrease system pressureafter the gaseous sample is pneumatically focused and injected into theseparatory column.
 25. The system of claim 23 where system pressure isincreased and decreased under computer control.
 26. The system of claim1 where the inline-pressure increasing device comprises a needle valveunder computer control.